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Bureau of Mines Information Circular/1983 




Explosives and Blasting Procedures 
Manual 



By Richard A. Dick, Larry R. Fletcher, 
and Dennis V. D'Andrea 



^ 
^ 



(i^Lo^ 



5=26^ »">u*5^ 



UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 8925 



Explosives and Blasting Procedures 
Manual 



By Richard A. Dick, Larry R. Fletcher, 
and Dennis V. D'Andrea 




UNITED STATES DEPARTMENT OF THE INTERIOR 
James G. Watt, Secretary 

BUREAU OF MINES 
Robert C. Norton, Director 



V 



.6 



v^^y^^ 



As the Nation's principal conservation agency, the Department of the Interior 
has responsibility for most of our nationally owned public lands and natural 
resources. This includes fostering the wisest use of our land and water re- 
sources, protecting our fish and wildlife, preserving the environmental and 
cultural values of our national parks and historical places, and providing for 
the enjoyment of life through outdoor recreation. The Department assesses 
our energy and mineral resources and works to assure that their development is 
in the best interests of all our people. The Department also has a major re- 
sponsibility for American Indian reservation communities and for people who 
live in Island Territories under U.S. administration. 



This publication has been cataloged as follows: 



Dick, Richard A 

Explosives and blasting procedures manual. 

(Bureau of Mines Information circular ; 8925) 

Supt. of Docs, no.: I 28.27:8925. 

1. Blasting— Handbooks, manuals, etc. 2. Explosives— Haudbooks, 
manuals, etc. I. Fletcher, Larry R. II. D' Andrea, Dennis V. III. 
Title. IV. Series: Information circular (United States. Bureau of 
Mines) ; 8925. 



~-TN295.U4 , [TN279] 622s [622'.23] 82-600353 



For sale by the Superintendent of Documents, U.S. Government Printing Office 
Washington, D.C. 20402 



CONTENTS 



Page 



Page 



Abstract 1 

Introduction 2 

Chapter 1 .—Explosives Products 

Chemistry and physics of explosives 3 

Types of explosives and blasting agents 4 

Nitroglycerin-based high explosives 5 

Dry blasting agents 7 

Slurries 9 

Two-component explosives 10 

Permissible explosives 11 

Primers and boosters 1 1 

Liquid oxygen explosive and black powder 13 

Properties of explosives 14 

Strength 14 

Detonation velocity 14 

Density 14 

Water resistance 15 

Fume class 15 

Detonation pressure 16 

Borehole pressure 16 

Sensitivity and sensitiveness 16 

Explosive selection criteria 17 

Explosive cost 17 

Charge diameter 18 

Cost of drilling 18 

Fragmentation difficulties 18 

Water conditions 18 

Adequacy of ventilation 18 

Atmospheric temperature 19 

Propagating ground 19 

Storage considerations - 19 

Sensitivity considerations 19 

Explosive atmospheres 20 

References 20 

Chapter 2. — Initiation and Priming 

Initiation systems 21 

Delay series 21 

Electric initiation 22 

Types of circuits 23 

Circuit calculations 25 

Power sources 25 

Circuit testing 28 

Extraneous electricity 30 

Additional considerations 30 

Detonating cord initiation 30 

Detonating cord products 31 

Field application 31 

Delay systems 33 

General considerations 34 

Detaline system 34 

Cap-and-fuse initiation 35 

Components 35 

Field applications 35 

Delays 36 

General considerations 36 

Other nonelectric initiation systems 36 

Hercudet 37 

None! 39 



Chapter 2. — Initiation and Priming — Con. 

Phming 43 

Types of explosive used 43 

Primer makeup 45 

Primer location 46 

Multiple priming 47 

References 47 

Chapter 3. — Blasthole Loading 

Checking the blasthole 49 

General loading procedures 49 

Small-diameter blastholes 50 

Cartridged products 50 

Bulk dry blasting agents 50 

Bulk slurries 52 

Permissible blasting 52 

Large-diameter blastholes 52 

Packaged products 52 

Bulk dry blasting agents 53 

Bulk slurries 54 

References 56 

Chapter 4. — Blast Design 

Properties and geology of the rock mass 57 

Characterizing the rock mass 57 

Rock density and hardness 57 

Voids and incompetent zones 57 

Jointing 58 

Bedding 58 

Surface blasting 59 

Blasthole diameter 59 

Types of blast patterns 61 

Burden 61 

Subdrilling 62 

Collar distance (stemming) 62 

Spacing 63 

Hole depth 64 

Delays.... 64 

Powder factor 65 

Secondary blasting 65 

Underground blasting 66 

Opening cuts 66 

Blasting rounds 68 

DeJays 69 

Powder factor 70 

Underground coal mine blasting 70 

Controlled blasting techniques 70 

Line drilling 70 

Presplitting 71 

Smooth blasting 73 

Cushion blasting 74 

References .- 74 

Chapter 5. — Environmental Effects of Blasting 

Flyrock 77 

Causes and alleviation 77 

Protective measures 77 



Page 
Chapter 5. — Environmental Effects of Blasting — Con. 

Ground vibrations 77 

Causes 78 

Prescrit}ed vibration levels and measurement 

techniques 79 

Scaled distance equation 80 

Reducing ground vibrations 80 

Airblast 80 

Causes 81 

Prescribed airblast levels and measurement 

techniques 82 

Reducing airblast 82 

Dust and gases 83 

References 83 

Chapter 6. — Blasting Safety 

Explosives storage 85 



Page 



Chapter 6.— Blasting Safety— Con. 



Transportation from magazine to jobsite 85 

PrecauTions befofeloading 86 

Primer preparation 88 

Borehole loading 88 

Hooking up the shot 90 

Shot firing 90 

Postshot safety 92 

Disposing of misfires 92 

Disposal of explosive materials 92 

Principal causes of blasting accidents 92 

Underground coal mine blasting 93 

References 93 

Bibliography 94 

Appendix A. — Federal blasting regulations 96 

Appendix B. — Glossary of terms used in explosives 

and blasting 99 



ILLUSTRATIONS 



1. Energy released by common products of detonation 3 

2. Pressure profiles created by detonation in a borehole 4 

3. Relative ingredients and properties of nitroglycerin-based high explosives 5 

4. Typical cartridges of dynamite 6 

5. Types of dry blasting agents and their ingredients 7 

6. Porous ammonium nitrate prills 8 

7. Water-resistant packages of AN-FO for use in wet boreholes 9 

8. Formulations of water-based products 10 

9. Slurry bulk loading trucks 11 

10. Loading slurry-filled polyethylene bags 12 

11. Cast primers for blasting caps and detonating cord 13 

12. Delay cast primer 13 

13. Effect of charge diameter on detonation velocity 14 

14. Nomograph for finding loading density 15 

15. Nomograph for finding detonation pressure 16 

16. Field mixing of AN-FO 17 

17. Instantaneous detonator 21 

18. Delay detonator 22 

19. Electric blasting caps 23 

20. Delay electric blasting cap 23 

21 . Types of electric blasting circuits 24 

22. Recommended wire splices 24 

23. Calculation of cap circuit resistance 25 

24. Capacitor discharge blasting machine 26 

25. Sequential blasting machine 27 

26. Blasting galvanometer 28 

27. Blasting multimeter 29 

28. Detonating cord 31 

29. Clip-on surface detonating cord delay connector 32 

30. Nonel surface detonating cord delay connector 32 

31 . Recommended knots for detonating cord 33 

32. Potential cutoffs from slack and tight detonating cord lines 33 

33. Typical blast pattern with surface delay connectors 33 

34. Misfire caused by cutoff from burden movement 34 

35. Blasting cap for use with safety fuse 35 

36. Cap, fuse, and Ignitacord assembly 36 

37. Hercudet blasting cap with 4-in tubes 37 

38. Extending Hercudet leads with duplex tubing 38 

39. Hercudet connections for surface blasting 38 

40. Hercudet pressure test module 39 



Page 
ILLUSTRATIONS— Continued 

41. Hercudet tester for small hookups 40 

42. Hercules bottle box and blasting machine 41 

43. Nonel blasting cap 41 

44. Nonel Primadet cap for surface blasting 42 

45. Nonel noiseless trunkline delay unit 42 

46. Noiseless trunkline using Nonel delay assemblies 42 

47. Nonel noiseless lead-in line 43 

48. Highly aluminized AN-FO booster 44 

49. Cartridge primed with electric blasting cap 45 

50. Priming cast primer with electric blasting cap 46 

51 . Priming blasting agents in large-diameter blastholes 47 

52. Corrective measures for voids 49 

53. Pneumatic loading of AN-FO underground 51 

54. Ejector-type pneumatic AN-FO loader 51 

55. AN-FO detonation velocity as a function of charge diameter and density 52 

56. Pouring slurry into small-diameter borehole 53 

57. Pumping slurry into small-diameter borehole 54 

58. Slurry leaving end of loading hose 55 

59. Loss of explosive energy through zones of weakness 58 

60. Effect of jointing on the stability of an excavation 58 

61. Tight and open corners caused by jointing 58 

62. Stemming through weak material and open beds 59 

63. Two methods of breaking a hard collar zone 59 

64. Effect of dipping beds on slope stability and potential toe problems 59 

65. Effect of large and small blastholes on unit costs 60 

66. Effect of jointing on selection of blasthole size 60 

67. Three basic types of drill pattern 61 

68. Corner cut staggered blast pattern — simultaneous initiation within rows 61 

69. V-echelon blast round 61 

70. Isometric view of a bench blast 61 

71 . Comparison of a 12y4-in-diameter blasthole (stiff burden) with a 6-in-diameter blasthole (flexible burden) in a 40-ft 

bench 62 

72. Effects of insufficient and excessive spacing 63 

73. Staggered blast pattern with alternate delays 63 

74. Staggered blast pattern with progressive delays 63 

75. The effect of inadequate delays between rows 64 

76. Types of opening cuts 66 

77. Six designs for parallel hole cuts 67 

78. Drill template for parallel hole cut 67 

79. Blast round for soft material using a sawed kerf 68 

80. Nomenclature for blastholes in a heading round 68 

81. Angled cut blast rounds 68 

82. Parallel hole cut blast rounds 68 

83. Fragmentation and shape of muckpile as a function of type of cut 69 

84. Fragmentation and shape of muckpile as a function of delay 69 

85. Typical burn cut blast round delay pattern 69 

86. Typical V-cut blast round delay pattern 69 

87. Shape of muckpile as a function of order of firing 69 

88. Stable slope produced by controlled blasting 71 

89. Crack generated by a presplit blast 72 

90. Three typical blasthole loads for presplitting 73 

91. Typical smooth blasting pattern 73 

92. Mining near a residential structure 75 

93. Example of a blasting record 76 

94. Seismograph for measuring ground vibrations from blasting 78 

95. Effects of confinement on vibration levels 79 

96. Effect of delay sequence on particle velocity 79 

97. Blasting seismograph with microphone for measuring airblast 81 

98. Causes of airblast 81 

99. Proper stacking of explosives 86 

100. AN-FO bulk storage facility 87 



Page 
ILLUSTRATIONS— Continued 

101 . Checking the rise of the AN-FO column with a weighted tape 89 

102. Blasting shelter 91 

TABLES 

1 . Properties of nitroglycerin-based explosives 5 

2. Fume classes designated by the Institute of Makers of Explosives 15 

3. Characteristics of pneumatically loaded AN-FO in small-diameter blastholes 52 

4. Approximate B/D ratios for bench blasting 62 

5. Approximate J/B ratios for bench blasting 62 

6. Typical powder factors for surface blasting 65 

7. Average specifications for line drilling 71 

8. Average specifications for presplitting 73 

9. Average specifications for smooth blasting 73 

10. Average specifications for cushion blasting 74 

1 1 . Maximum recommended airblast levels 82 

A-1 . Federal regulatory agency responsibility 96 



UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 



amp 


ampere 


ft 


foot 


cm 


centimeter 


g 


gram 


cucm 


cubic centimeter 


gr 


grain 


cuft 


cubic foot 


Hz 


hertz 


cuyd 


cubic yard 


in 


inch 


dB 


decibel 


kb 


kilobar 


° 


degree 


kcal 


kilocalorie 


°F 


degree Fahrenheit 


lb 


pound 


tps 


foot per second 


mi 


mile 



mm 


minute 


ms 


millisecond 


pet 


percent 


ppm 


parts per million 


psi 


pound per square inch 


sec 


second 


sqft 


square foot 


sqin 


square inch 


yd 


yard 



EXPLOSIVES AND BLASTING PROCEDURES MANUAL 

By Richard A. Dick,^ Larry R. Fletcher,^ and Dennis V. D' Andrea^ 

ABSTRACT 



This Bureau of Mines report covers the latest technology in explosives and blasting 
procedures. It includes information and procedures developed by Bureau research, explo- 
sives manufacturers, and the mining industry. It is intended for use as a guide in developing 
training programs and also to provide experienced blasters an update on the latest state of 
technology in the broad field of explosives and blasting. 

Types of explosives and blasting agents and their key explosive and physical properties 
are discussed. Explosives selection criteria are described. The features of the traditional 
initiation systems — electrical, detonating cord, and cap and fuse — are pointed out, and the 
newer nonelectric initiation systems are discussed. Various blasthole priming techniques 
are described. Blasthole loading of various explosive types is covered. Blast design, includ- 
ing geologic considerations, for both surface and underground blasting is detailed. Environmental 
effects of blasting such as flyrock and air and ground vibrations are discussed along with 
techniques of measuring and alleviating these undesirable side effects. Blasting safety 
procedures are detailed in the chronological order of the blasting process. 

The various Federal blasting regulations are enumerated along with their Code of Federal 
Regulations citations. An extensive glossary of blasting related terms is included along with 
references to articles providing more detailed information on the aforementioned items. 
Emphasis in the report has been placed on practical considerations. 

^Mining engineer, Twin Cities Research Center, Bureau of Mines, Minneapolis, MN. 

^Mining engineering technician. Twin Cities Research Center, Bureau of Mines, Minneapolis, MN. 

^Supervisory physical scientist. Twin Cities Research Center, Bureau of Mines, Minneapolis, MN. 



INTRODUCTION 

The need for better and more widely available blasters' training has long been recognized in the 
blasting confimunity. The Mine Safety and Health Administration (MSHA) of the Department of Labor 
requires health and safety training for blasters. In 1980, the Office of Surface Mining Reclamation and 
Enforcement (OSM), Department of the Interior, promulgated regulations for the certification of 
blasters in the area of environmental protection. These regulations are certain to have a positive 
influence on the level of training and competence of blasters. They will, however, present a problem to 
the mining industry. That problem is a scarcity of appropriate training material. Although numerous 
handbooks and textbooks are available (9, 24, 27, 29-30, 32, 46f none are geared for use in training 
the broad spectrum of people involved in practical blasting. This manual is designed to fulfill that need. 

It is appropriate that the Bureau of Mines prepare such a manual. Since its inception, the Bureau has 
been involved in all aspects of explosives and blasting research including productivity, health and 
safety, and environment, and has provided extensive technical assistance to industry and regulatory 
agencies in the promotion of good blasting practices. 

This manual serves two basic functions. The first is to provide a source of individual study for the 
practical blaster. There are literally tens of thousands of people involved in blasting at mines in the 
country and there are not enough formal training courses available to reach the majority of them. The 
second function is to provide guidance to industry, consultants, and academic institutions in the 
preparation of practical training courses on blasting. 

The manual has been broken down into a series of discrete topics to facilitate self-study and the 
preparation of training modules. Each section stands on its own. Each student or instructor can utilize 
only those sections that suit his or her needs. An attempt has been made to provide concise, yet 
comprehensive coverage of the broad field of blasting technology. Although liberal use has been made 
of both Bureau and non-Bureau literature in preparation of this manual, none of the topics are dealt with 
in the depth that would be provided by a textbook or by a publication dealing with a specific topic. Each 
section is supplemented by references that can be used to pursue a more in-depth study. These 
references are limited to practical items that are of direct value to the blaster in the field. Theory is 
included only where it is essential to the understanding of a concept. 

Where methods of accomplishing specific tasks are recommended, these should not be considered 
the only satisfactory methods. In many instances there is more than one safe, effective way to 
accomplish a specific blasting task. 

None of the material in this manual is intended to replace manufacturers' recommendations on the 
use of the products involved. It is strongly recommended that the individual manufacturer be consulted 
on the proper use of specific products. 

^Italicized numbers in parentheses refer to items in the bibliography preceding the appendixes. 



Chapter 1 .—EXPLOSIVES PRODUCTS 



CHEMISTRY AND PHYSICS OF EXPLOSIVES 



It is not essential that a blaster have a strong knowledge of 
chemistry and physics. However, a brief discussion of the 
reactions of explosives will be helpful in understanding how 
the energy required to break rock is developed. 

An explosive is a chemical compound or mixture of compounds 
that undergoes a very rapid decomposition when initiated by 
energy in the form of heat, impact, friction, or shock (4)\ This 
decomposition produces more stable substances, mostly gases, 
and a large amount of heat. The very hot gases produce 
extremely high pressures within the borehole, and it is these 
pressures that cause the rock to be fragmented. If the speed of 
reaction of the explosive is faster than the speed of sound in 
the explosive (detonation), the product is called a high explosive. If 
the reaction of the explosive is slower than the speed of sound 
in the explosive (deflagration), the product is called a low 
explosive. 

The principal reacting ingredients in an explosive are fuels 
and oxidizers. Common fuels in commercial products include 
fuel oil, carbon, aluminum, TNT, smokeless powder, 
monomethylamine nitrate, and monoethanol amine nitrate. 
Fuels often perform a sensitizing function. Common explosive 
sensitizers are nitroglycerin, nitrostarch, aluminum, TNT, 
smokeless powder, monomethylamine nitrate, and monoethal- 
amine nitrate. Microballoons and aerating agents are sometimes 
added to enhance sensitivity. The most common oxidizer is 
ammonium nitrate, although sodium nitrate and calcium nitrate 
may also be used. Other ingredients of explosives include 
water, gums, thickeners and cross-linking agents used in slurries 
(11), gelatinizers, densifiers, antacids, stabilizers, absorbents, 
and flame retardants. In molecular explosives such as 
nitroglycerin, TNT, and PETN, the fuel and oxidizer are combined 
in the same compound. 

Most ingredients of explosives are composed of the elements 
oxygen, nitrogen, hydrogen, and carbon. In addition, metallic 
elements such as aluminum are sometimes used. For explosive 
mixtures, energy release is optimized at zero oxygen balance 
(5 ). Zero oxygen balance is defined as the point at which a 
mixture has sufficient oxygen to completely oxidize all the 
fuels it contains but there is no excess oxygen to react with the 
nitrogen in the mixture to form nitrogen oxides. 

Theoretically, at zero oxygen balance the gaseous products 
of detonation are H2O, CO2, and N2, although in reality small 
amounts of NO, CO, NH2, CH4, and other gases are generated. 
Figure 1 shows the energy released by some of the common 
products of detonation. Partial oxidation of carbon to carbon 
monoxide, which results from an oxygen deficiency, releases 
less heat than complete oxidation to carbon dioxide. The 
oxides of nitrogen, which are produced when there is excess 
oxygen, are "heat robbers;" that is, they absorb heat when 
generated. Free nitrogen, being an element, neither absorbs 
nor releases heat upon liberation. 

It should be noted that the gases resulting from improper 
oxygen balance are not only inefficient in terms of heat energy 
released but are also poisonous. Although the oxidation of 
aluminum yields a solid, rather than a gaseous, product the 

' Italicized numbers in parentheses refer tp items in the list of references at the 
end of this chapter. 



WJ 



^ 



Figure 1. — Energy released by common products of 
detonation. 



large amount of heat released adds significantly to the explosive's 
energy. Magnesium is even better from the standpoint of heat 
release, but is too sensitive to use in commercial explosives. 
The principle of oxygen balance is best illustrated by the 
reaction of ammonium nitrate-fuel oil [(NH4N03)-(CH2) J mixtures. 
Commonly called AN-FO, these mixtures are the most widely 
used blasting agents. From the reaction equations for AN-FO, 
one can readily see the relationship between oxygen balance, 
detonation products, and heat release. The equations assume 
an ideal detonation reaction, whifeh in turn assumes thorough 
mixing of ingredients, proper particle sizing, adequate 
confinement, charge diameter and priming, and protection 
from water. Fuel oil is actually a variable mixture of hydrocartx}ns 
and is not precisely CH2, but this identification simplifies the 
equations- and is accurate enough for the purposes of this 
manual. In reviewing these equations, keep in mind that the 
amount of heat produced is a measure of the energy released. 



(94.5 pet AN)— (5.5 pet FO): 

3NH4NO3 + CH2— >7H20 + 
CO2 + 3N2 + 0.93 kcal/g. 

(92.0 pet AN)— (8.0 pet FO): 

2NH4NO3 + CH2— >5H20 + 
CO + 2N2 + 0.81 kcal/g. 



(96.6 pet AN)— (3.4 pet FO): 
5NH4NO3 + CH2 



.IIH2O + CO, + 



4N2 + 2N0 + 0.60 kcal/g. 



(1) 



(2) 



(3) 



Equation 1 represents the reaction of an oxygen-balanced 
mixture containing 94.5 pet AN and 5.5 pet FO. None of the 
detonation gases are poisonous and 0.93 kcal of heat is 
released for each gram of AN-FO detonated. In equation 2, 
representing a mixture of 92.0 pet AN and 8.0 pet FO, the 
excess fuel creates an oxygen deficiency. As a result, the 



carbon in the fuel oil is oxidized only to CO, a poisonous gas, 
rather than relatively harmless CO2. Because of the lower heat 
of formation of CO, only 0.81 kcal of heat is released for each 
gram of AN-FO detonated. In equation 3, the mixture of 96.6 
pet AN and 3.4 pet FO has a fuel shortage that creates an 
excess oxygen condition. Some of the nitrogen from the 
ammonium nitrate combines with this excess oxygen to form 
NO, which will react with oxygen in the atmosphere to form 
extremely toxic NO2. The heat absorbed by the formation of 
NO reduces the heat of reaction to only 0.60 kcal, which is 
considerably lower than that of an overt ueled mixture. Also the 
CO produced by an overfueled mixture is less toxic than NO 
and NO2. For these reasons a slight oxygen deficiency is 
preferable and the common AN-FO mixture for field use is 94 
pet AN and 6 pet FO. 

Although the simple AN-FO mixture is optimum for highest 
energy release per unit cost of ingredients, products with 
higher energies and densities are often desired. The common 
high-energy producing additives, which may be used in both 
dry blasting agents and slurries, fall into two basic categories: 
explosives, such as TNT, and metals, such as aluminum. 
Equations 4 and 5 illustrate the reaction of TNT and aluminum 
as fuel-sensitizers with ammonium nitrate. The reaction products, 
again, assume ideal detonation, which is never actually attained 
in the field. In practice, aluminum is never the only fuel in the 
mixture, some carbonaceous fuel is always used. 

(78.7 pet AN)— (21 .3 pet TNT): 

2INH4NO3 + 2C6H2CH3(N02)3— >47H20 - 
14CO2 + 24N2+ 1.01 kcal/g. 



(4) 



(81.6pctAN)— (18.4petAI): 

3NH4NO3 + 2AI— >6H20 + 
AI2O3 + 3N2 + 1.62 kcal/g. 



(5) 



Both of these mixtures release more energy, based on 
weight, than ammonium nitrate-carbonaceous fuel mixtures 
and have the added benefit of higher densities. These 
advantages must be weighed against the higher cost of such 
high-energy additives. The energy of aluminized products 
continues to increase with larger percentages of metal, even 
though this "overfueling" causes an oxygen deficiency. 
Increasing energy by overfueling with metals, however, is 
uneconomical except for such specialty products as high- 
energy boosters. 

The chemical reaction of an explosive creates extremely 
high pressures. It is these pressures which cause rock to be 
broken and displaced. To illustrate the pressures created in 
the borehole, a brief look will be taken at the detonation 
process as pictured by Dr. Richard Ash of the University of 
Missouri-Rolla. Figure 2, adapted from Ash's work shows (top) 
a column of explosive or blasting agent that has been initiated. 
Detonation has proceeded to the center of the column. The 



/""'"'"" 



Vp,.3,„„,, 




Figure 2.— Pressure profiles created by detonation 
in a borehole. 



primary reaction occurs between a shock front at the leading 
edge and a rear boundary known as the Chapman-Jouguet 
(C-J) plane. Part of the reaction may occur behind the C-J 
plane, particularly if some of the explosive's ingredients are 
coarse. The length of the reaction zone, which depends on the 
explosive's ingredients, particle size, density, and confinement, 
determines the minimum diameter at which the explosive will 
function dependably (critical diameter). High explosives, which 
have short reaction zones, have smaller critical diameters 
than blasting agents. 

The pressure profiles in figure 2 (bottom) show the explosive 
forces applied to the rock being blasted. A general comparison 
is given between an explosive and a blasting agent, although it 
should be understood that each explosive or blasting agent 
has its own particular pressure profile depending on its 
ingredients, particle size, density, and confinement. 

The initial pressure, called the detonation pressure {PJ, is 
created by the supersonic shock front moving out from the 
detonation zone. The detonation pressure gives the explosive 
its shattering action in the vicinity of the borehole. If the explosive 
reacts slower than the speed of sound, which is normally the 
case with black powder, there is no detonation pressure. 

The detonation pressure is followed by a sustained pressure 
called explosion pressure (P), or txjrehole pressure. Borehole 
pressure is created by the rapid expansion of the hot gases 
within the borehole. The detonation pressure of high explosives 
is often several times that of blasting agents, but the borehole 
pressures of the two types of products are of the same general 
magnitude. The relative importance of detonation pressure 
and borehole pressure in breaking rock will be discussed in 
the "Properties of Explosives" section of this chapter. 



TYPES OF EXPLOSIVES AND BLASTING AGENTS 



This section will cover all explosive products that are used 
for industrial rock blasting, with the exception of initiators. 
Products used as the main borehole charge can be divided 
into three categories: nitroglycerin- (or nitrostarch-) based 
high explosives, dry blasting agents, and slurries, which may 
also be referred to as water gels or emulsions. These products 
can also be broadly categorized as explosives and blasting 



agents. For ease of expression, the term explosives will often 
be used in this manual to collectively cover both explosives 
and blasting agents. The difference between an explosive and 
a blasting agent is as follows. 

A high explosive is any product used in blasting that is 
sensitive to a No. 8 cap and that reacts at a speed faster than 
the speed of sound in the explosive medium. A low explosive 



is a product in whicfi tfie reaction is slower than the speed of 
sound. Low explosives are seldom used in blasting today. A 
blasting agent is any material or mixture consisting of a fuel 
and an oxidizer, intended for blasting, not othenn/ise classified 
as an explosive, provided that the finished product, as mixed 
and packaged for shipment, cannot be detonated by a No. 8 
blasting cap in a specific test prescribed by the Bureau of 
Mines. Slurries containing TNT, smokeless powder, or other 
explosive ingredients, are classed as blasting agents if they 
are insensitive to a No. 8 blasting cap. 

AN-FO, which in normal form is a blasting agent, can be 
made cap sensitive by pulverizing it to a fine particle size, and 
a slurry can be made cap sensitive by including a sufficient 
amount of finely flaked paint-grade aluminum. Although neither 
of these products contains an explosive ingredient, their cap 
sensitivity requires their being classified as explosives. The 
term nitrocarbonitrate, or NCN, was once used synonymously 
with blasting agent under U.S. Department of Transportation 
(DOT) regulations for packaging and shipping blasting agents. 
DOT no longer uses this term. 



NITROGLYCERIN-BASED 
HIGH EXPLOSIVES 

Nitroglycerin-based explosives can be categorized as to 
their nitroglycerin content (4). Figure 3 shows this breakdown 



Gelolinous Pfope 



Nitroglycerin 


Blosting gelatin 


Straight dynomite 


Straight gelatin 


High-density 
ammonia dynamite 


Ammonia gelatin 


Low-density 
ammonia dynamite 


Semtgelotin 




Dry blasting agents 







Figure 3. — Relative ingredients and properties of 
nitroglycerin-6ased high explosives. 



along with some relative properties and ingredients of these 
products. Table 1 shows some properties of nitroglycerin- 
based explosives. Property values are averages of manufac- 
turers' published figures. As a group, nitroglycerin-based 
explosives are the most sensitive commercial products used 
today (excluding detonators). Because of this sensitivity they 
offer an extra margin of dependability in the blasthole but are 
somewhat more susceptible to accidental detonation. This is a 
tradeoff that many operators using small-diameter boreholes 







Table 1. - Properties of nitroglycerin-based explosives 




Weight 

strength, 

pet 


Bulk 

Strength, 

pet 


Speeific 
gravity 


Detonation 

veloeity, 

fps 


Water 
resistance 


Fume 
class 


STRAIGHT DYNAMITE 


50 


50 


1.4 


17,000 


Good 


Poor. 


HIGH-DENSITY AMMONIA DYNAMITE 


60 
40 
20 


50 
35 

15 


1.3 
1.3 
1.3 


12,500 
10,500 
8,000 


Fair 

...do 

...do 


Good. 
Do. 
Do. 


LOW-DENSITY AMMONIA DYNAMITE, HIGH VELOCITY 


65 
65 
65 
65 


50 
40 
30 
20 


1.2 
1.0 
.9 
.8 


11,000 
10,000 
9,500 
8,500 


Fair 

...do 

Poor 

...do 


Fair. 
Do. 
Do. 
Do. 


LOW-DENSITY AMMONIA DYNAMITE, LOW VELOCITY 


65 
65 
65 
65 


50 
40 
30 
20 


1.2 
1.0 
.9 
.8 


8,000 
7,500 
7,000 
6,500 


Fair 

Poor 

...do 

...do 


Fair 
Do. 
Do. 
Do. 


BLASTING GELATIN 


100 


90 


1.3 


25,000 


Excellent 


Poor. 


STRAIGHT GELATIN 


90 
60 
40 
20 


80 
60 

45 
30 


1.3 
1.4 
1.5 
1.7 


23,000 
20,000 
16,500 
11,000 


Excellent 

....do 

....do 

....do 


Poor. 
Good. 

Do. 

Do. 


AMMONIA GELATIN 


80 


70 
60 

45 


1.3 
1.4 
1.5 


20,000 
17,500 
16,000 




Good. 


60 
40 


...do 

...do 


Very good. 
Do, 


SEMIGELATIN 


65 


60 
50 
40 
30 


1.3 
1.2 
1,1 
.9 


12,000 
12,000 
1 1 ,500 
10,500 




Very good. 
Do. 
Do. 
Do. 


65 
65 
65 


...do 

Good 

Fair 



must make. Nitroglycerin dynamites account for less than 5 
pet, by weight, of the explosives market (72 ), and almost all of 
that is in small-diameter work. Dynamite is available in cartridges 
of various sizes and shapes, as shown in figure 4. 



Nitroglycerin (NG), the first high explosive, is the sensitizer 
in dynamites and is seldom used alone, although it has been 
used in a somewhat desensitized form for shooting oil wells. It 
has a specific gravity of 1 .6 and a detonation velocity slightly 




Figure 4.— Typical cartridges of dynamite. (Courtesy Atlas Powder co.) 



over 25,000 fps. Its extreme sensitivity to shock, friction, and 
heat make it hazardous to use. 

Straight (nitroglycerin) dynamite consists of nitroglycerin, 
sodium nitrate, an antacid, a cartjonaceous fuel, and sometimes 
sulfur. The term "straight" means that a dynamite contains no 
ammonium nitrate. The weight strength, usually 50 pet, indicates 
the approximate percentage of nitroglycerin or other explosive 
oil. The use of straight dynamite is limited because of its high 
cost and sensitivity to shock and friction. Fifty percent straight 
dynamite, by far the most common straight dynamite, is referred 
to as ditching dynamite and is used in propagation blasting. 

High-density ammonia dynamite, also called extra dynamite, 
is the most widely used dynamite. It is like straight dynamite, 
except that ammonium nitrate replaces part of the nitroglycerin 
and sodium nitrate. Ammonia dynamite is manufactured in 
grades of 20 to 60 pet weight strength, although these grades 
are not truly equivalent to straight dynamites of the same 
weight stength (see properties in table 1 ). Ammonia dynamite 
is less sensitive to shock and friction than straight dynamite. It 
is most commonly used in small quarries, in underground 
mines, in construction, and as an agricultural explosive. 

Low-density ammonia dynamite is manufactured in a weight 
strength of about 65 pet. The cartridge (bulk) strength ranges 
from 20 to 50 pet, depending on the bulk density of the ingredients. 
A high-vekx% series and a low-vekx:ity series are manufactured. 
Low-density ammonia dynamite is useful in very soft or 
prefraetured rock or where coarse rock such as riprap is 
required. 

Blasting gelatin is a tough, rubber-textured explosive made 
by adding nitrocellulose, also called guncotton, to nitroglycerin. 
An antacid is added to provide storage stability and wood meal 
is added to improve sensitivity. Blasting gelatin emits large 
volumes of noxious fumes upon detonation and is expensive. 
It is seldom used today. Sometimes called oil well explosive, it 
has been used in deep wells where high heads of water are 
encountered. Blasting gelatin is the most powerful nitroglycerin- 
based explosive. 

Straight gelatin is basically a blasting gelatin with sodium 
nitrate, carbonaceous fuel, and sometimes sulfur added. It is 
manufactured in grades ranging from 20 to 90 pet weight 
strength and is the gelatinous equivalent of straight dynamite. 
Straight gelatin has been used mainly in specialty areas such 
as seismic or deep well work, where a lack of confinement or a 
high head of water may affect its velocity. To overcome these 
conditions a high-velocity gelatin is available which is like 
straight gelatin except that it detonates near its rated velocity 
despite high heads of water. 

Ammonia gelatin, also called special gelatin or extra gelatin, 
is a straight gelatin in which ammonium nitrate has replaced 
part of the nitroglycerin and sodium nitrate. Manufactured in 
weight strengths ranging from 40 to 80 pet, it is the gelatinous 
equivalent of ammonia dynamite. Ammonia-gelatin is suitable 
for underground work, in wet conditions, and as a toe load, 
primarily in small-diameter boreholes. The higher grades (70 
pet or higher) are useful as primers for blasting agents. 

Semigelatin has a weight strength near 65 pet. The cartridge 
(bulk) strength ranges from 30 to 60 pet with variations in the 
bulk density of the ingredients. Semigelatin is versatile and is 
used in small-diameter work where some water resistance is 
required. It is useful underground, where its soft, plastic 
consistency makes it ideal for loading into holes drilled upward. 

Nitrostarch explosives are sensitized with nitrostarch, a 
solid molecular explosive, rather than an explosive oil. They 
are manufactured in various grades, strengths, densities, and 
degrees of water resistance to compete with most grades of 
nitroglycerin-based dynamites. They are similar to dynamites 



in many ways with their most significant differences being 
somewhat higher impact resistance and their "headache-free" 
nature. 

DRY BLASTING 
AGENTS 

In this manual, the term dry blasting agent describes any 
material used for blasting which is not cap sensitive and in 
which water is not used in the formulation. Figure 5 describes 
the dry blasting agents in use today. 

Early dry blasting agents employed solid carbon fuels 
combined with ammonium nitrate in various forms. Through 
experimentation it was found that diesel fuel oil mixed with 
porous ammonium nitrate prills (fig. 6) gave the best blasting 
results. Hence, the term AN-FO (ammonium nitrate-fuel oil) 
has been synonymous with dry blasting agent. An oxygen- 
balanced AN-FO is the cheapest source of explosive energy 
available today. Adding finely divided or flaked aluminum to 
dry blasting agents increases the energy output but at an 
increase in cost. Aluminumized dry mixes are sometimes 
used in combination with cast primers as primers for AN-FO. 
Aluminized mixes may also be used as a high-energy toe load 
and as the main column charge where blasting is difficult. 



Ammonium nitrate 



I Fuel, I 

I usually fuel oil I 



Densifying 
agent 



I. 



Pulverized 
prills 



J 



I Aluminum | 
I I 



Dry 

blasting 

agent 

(AN-FO) 



Densified 

dry 
blasting 
agent 



Aluminized 

dry 

blasting 

agent 



Figure 5.— Types of dry blasting agents and their 
Ingredients. 




Figure 6.— Porous ammonium nitrate prills. (Courtesy Hercules inc.) 



It is difficult to give precise numerical values for the properties 
of dry blasting agents because the properties vary with ingredient 
particle size, density, confinement, charge diameter, water 
conditions, and coupling ratio (5). Yancik has prepared an 
excellent manual on explosive properties of AN-FO (9). 

Coupling ratio is the percentage of the borehole diameter 
filled with explosive. Poured bulk products are completely 
coupled, which increases their efficiency. Cartridged products 
are partially decoupled, and thus lose some efficiency. 

AN-FO's theoretical energy is optimized at oxygen balance 
(approximately 94.5 pet AN and 5.5 pet FO), where the detonation 
velocity approaches 15,000 fps in large charge diameters. 
Excess fuel oil (8 pet or more) can seriously reduce sensitivity 
to initiation. Inadequate fuel oil causes an excess of harmful 
nitrogen oxide fumes in the detonation gases. Specific gravities 
of AN-FO range from 0.5 to 1.15; 0.80 to 0.85 is the most 
common range. The lighter products are useful in easily 
fragmented rock or to eliminate the need for alternate decks of 
explosive and stemming where a low powder factor is desirable. 
The densified dry mixes are packaged in waterproof containers 
for use in wet blastholes (fig. 7). 

Densification is necessary to enable the cartridges to sink in 
water. To obtain a higher specific gravity, part of the prills are 
pulverized and thsn the mixture of whole and pulverized prills 
is vibrated or othenwise compressed into rigid cartridges or 



polyburlap bags. Densifying ingredients, such as ferrosilicon, 
are seldom used today because they add little or nothing to the 
explosive's energy. The sensitivity of AN-FO decreases with 
increased density. The "dead press" limit, above which 
detonation is undependable, is about 1 .25 g/cu cm. 

The detonation velocity of AN-FO is strongly affected by 
charge diameter. The critical diameter is near 1 in with a 
normal prill and oil mixture. The velocity increases with diameter 
and levels off near a 15-in diameter at a velocity of nearly 
1 5,000 fps. The minimum primer required for AN-FO increases 
as charge diameter increases. There is a tendency to underprime 
in large-diameter boreholes. A good rule of thumb is, when in 
doubt, overprime. Many operators claim improved results when 
they use primers that fill, or nearly fill, the blasthole diameter. 

The undesirable errect of water on dry blasting agents has 
often been seen in poor blasts where AN-FO was used in wet 
boreholes with insufficient external protection. Excess water 
adversely affects the velocity, sensitivity, fume class, and 
energy output of a dry blasting agent. The extreme result is a 
misfire. It is essential when using AN-FO in wet conditions that 
positive protection in the form of a waterproof package or a 
borehole liner be used (3). 

Dry blasting agents can be purchased in four forms. In 
increasing order of cost they are as follows: 




Figure 7.— Water-resistant paclcages of AN-FO for use in wet borelioles. (Courtesy Gulf on Chemicals Co.) 



1 . As separate ingredients in bulk form for onsite mixing 

2. Premixed in bull< form for onsite storage or direct borehole 
delivery (a premixed product may cost about the same as 
separate ingredients). 

3. In paper or polyethylene packages for pouring into the 
borehole. 

4. in waterproof cartridges or polyburlap containers. 

Waterproof containers are the most expensive forms and 
eliminate the advantage of direct borehole coupling. They 
should be used only where borehole conditions dictate. Because 
improper ingredient proportions or an insufficiently mixed product 
cause inefficient detonation and poor fume qualities, thorough 
mixing and close quality control should be exercised in an 
onsite mixing operation. The use of a colored dye in the fuel 
gives a visual check on mixing and also makes the blasting 
agent more easily visible in case of misfire. 

Recent trials in taconite mines have employed a dense dry 
blasting agent composed of 87 pet crushed ammonium nitrate 
prills and 1 3 pet of a 50-50 mixture of nitropropane and methanol. 
This product has slightly more energy per unit weight than 
AN-FO and can be loaded at a density of approximately 1 .2 
g/cu cm, giving it a high energy density. Because of the 
experimental nature of this product, MSHA should be consulted 
before putting it to use. 



SLURRIES 

A slurry (fig.8) is a mixture of nitrates such as ammonium 
nitrate and sodium nitrate, a fuel sensitizer, either explosive or 
nonexplosive, and varying amounts of water (7). A water gel is 
essentially the same as a slurry and the two terms are frequently 
used interchangeably. An emulsion is somewhat different from 
a water gel or slurry in physical character but similar in many 
functional respects. The principal differences are an emulsion's 
generally higher detonation velocity and a tendency to wet or 
adhere td the blasthole, which in some cases may affect its 
bulk loading characteristics. In this discussion, slurries, water 
gels, and emulsions will be treated as a family of products. 

Although they contain large amounts of ammonium nitrate, 
slurries are made wator resistant through the use of gums, 
waxes, and cross-linking agents. The variety of possible slurry 
formulations is almost infinite. Frequently a slurry is specially 
formulated for a specific job. The list of possible fuel sensitizers 
is especially long (7 7), although carbonaceous fuels, aluminum, 
and amine nitrates are the most common. 

Slurries may be classified as either explosives or blasting 
agents. Those that are sensitive to a No. 8 cap are classified 
as explosives, even though they are less sensitive than 
dynamites. It is important that slurries be stored in magazines 
appropriate to their classification. 



10 



Ammonium nitrate 



Inorganic nitrate (sometimes), water, 
gums, thickener, fuel (carbonaceous) 



Ai..n„i„..n,. ' ' smokeless I 

I Aluminum i i . i 

I I I powder, I 

I I nitrostarch I 



Aluminized 

water gel 

blasting 

agent 



Explosive- 
sensitized 

large - 
diameter 
water gel 




I Aluminum, 

amine nitrate, 
I microbailoon, 
I other sensitizer I 



I Stabilizer 



Small- 
diameter 
water gel 
explosive 



Air-sensitized 

water gel 
blasting agent 



Figure 8.— Formulations of water-based products. 



Except for their excellent water resistance and higher density 
and bulk strength, slurries are similar in many ways to dry 
blasting agents. Good oxygen balance, decreased particle 
size and increased density, increased charge diameter, good 
confinement and coupling, and adequate priming all increase 
their efficiency. Although slurry blasting agents tend to lose 
sensitivity as their density increases, some explosive-based 
slurries function well at densities up to 1.6. The effect of 
charge diameter on the detonation velocity of slurries is not as 
pronounced as it is on AN-FO. 

Most non-cap-sensitive slurnes depend on entrapped air for 
their sensitivity and most cap-sensitive varieties are also 
dependent, to a lesser degree, on this entrapped air. If this air 
is removed from a slurry through pressure from an adjacent 
blast, prolonged periods of time in the borehole, or prolonged 
storage, the slurry may become desensitized. 



Slurries can be delivered as separate ingredients for onsite 
mixing, premixed for bulk loading (fig. 9), in polyethylene bags 
for bulk loading or loading in the bag (fig. 1 0), or they may be 
cartridged. Their consistency may be anywhere from a liquid 
to a cohesive gel. 

Cartridged slurries for use in small-diameter blastholes (2-in 
diameter or less) are normally made cap sensitive so they can 
be substituted for dynamites. However, their lower sensitivity 
as compared with dynamite should be kept in mind. The 
sensitivity and performance of some grades of slurries are 
adversely affected by low temperatures. Slurries designed for 
use in medium-diameter blastholes (2- to 5-in diameters) may 
be cap sensitive but.they often are not. Those that are not cap 
sensitive must be primed with a cap-sensitive explosive. Slurries 
for use in large diameters (greater than 5 in) are the least 
sensitive slurries. 

Slurries containing neither aluminum nor explosive sensitizers 
are the cheapest, but they are also the least dense and powerful. 
In wet conditions where dewatering is not practical, and the 
rock is not extremely difficult to fragment, these low-cost slurries 
offer competition to AN-FO. 

Aluminized slurries or those containing significant amounts 
of other high-energy sensitizers, develop sufficient energy for 
blasting in hard, dense rock. However, the economics of using 
total column charges of highly aluminized slurry are doubtful 
because of the significantly higher cost of these products. 
High-energy slurries have improved blasting efficiency when 
used in combination with the primer at the toe or in another 
zone of difficult breakage. 

Detonating cord downlines can have a harmful effect on the 
efficiency of blasting agent slurries, depending on the size of 
the blasthole and the strength of the cord. When using detonat- 
ing cord downlines, the slurry manufacturer should be con- 
sulted concerning the effect of the cord on the slurry. 

The technology of slurries is very dynamic. New products 
are continually being developed. The blaster should check the 
technical literature to be aware of developments that affect his 
or her blasting program. 



TWO-COMPONENT 
EXPLOSIVES 

Individually, the components of two-component explosives, 
also called binary explosives, are not classified as explosives. 
When shipped and stored separately they are not normally 
regulated as explosives, but they should be protected from 
theft. However, some organizations such as the U.S. Forest 
Service, and some State and local government agencies, may 
treat these components as explosives for storage purposes. 

The most common two-component explosive is a mixture of 
pulverized ammonium nitrate and nitromethane, although other 
fuel sensitizers such as rocket fuel have been used. The 
components are carried in separate containers to the jobsite, 
where the container of liquid fuel is poured into the ammonium 
nitrate container. After the prescribed waiting time the mixture 
becomes cap sensitive and is ready for use. 

Two-component explosives are sometimes used where only 
small amounts of explosives are required such as in poweriine 
installation and light construction. Where large amounts of 
explosives are needed, the higher cost per pound and the 
inconvenience of onsite mixing negate the savings and conven- 
ience realized through less stringent storage and distribution 
requirements. In some States, for example Pennsylvania, the 
user of two-component explosives is considered a manufac- 
turer and must obtain a manufacturer's license. 



11 




Figure 9.— Slurry bulk loading trucks. (Courtesy Gulf on chemicals Co.) 



PERMISSIBLE 
EXPLOSIVES 



7. The explosive must exhibit insensitivity in the pendulum 
friction test. 



Permissible explosives are designed for use in underground 
coal mines, where the presence of explosive gases or dust 
presents an abnormal blasting hazard. Both nitroglycerin-based 
permissibles and slurry, water gel, and emulsion permissibles 
are available. Briefly stated, the specifications of a permissible 
explosive are as follows: 

1. The chemical composition furnished by the applicant 
must agree, within tolerance, with that determined by MSHA. 

2. The explosive must pass a series of propagation tests. 

3. The airgap sensitivity of rA-in cartridges must be at 
least 3 in. 

4. The explosive must pass nonignition tests when fired 
unstemmed into a mixture of natural gas, air, and bituminous 
coal dust. 

5. The explosive must pass tests for nonignition when fired 
stemmed in a gallery of air and natural gas. 

6. The volume of poisonous gases produced by a pound of 
explosive must not exceed 2.5 cu ft. 



Permissible explosives must be used in a permissible manner, 
as described briefly in the "Underground Coal Mine Blasting" 
section of chapter 4. MSHA must also approve explosives 
used in gassy noncoal mines. For gassy noncoal mines, MSHA 
sometimes approves products such as AN-FO, and specifies 
the manner in which they are to be used. 

Sodium chloride or other flame depressants are used in 
permissible explosives to minimize the chance of igniting the 
mine atmosphere. As a result, permissible explosives are less 
energetic than other explosives and have a lower rock-breaking 
capability. They should be used only where required by a 
gassy atmosphere. Permissible explosives are allowed to gener- 
ate more fumes than other explosives, but most do not. MSHA 
periodically publishes an up-dated list of brand names and 
properties of permissible explosives (14). 



PRIMERS AND 
BOOSTERS 

The terms "primer" and "booster" are often confused. Accord- 
ing to MSHA a primer, sometimes called a capped primer, is a 
unit of cap-sensitive explosive used to initiate other explosives 
or blasting agents. A primer contains a detonator. A booster is 



12 




Figure 10. — Loading slurry-filled polyethylene bags. (Courtesy Atlas Powder Co.) 



often, but not always, cap sensitive, but does not contain a 
detonator. A booster is used to perpetuate or intensify an 
explosive reaction. 

Although various products have been used as primers and 
boosters, an explosive with a high detonation pressure such 
as a high-strength ammonia gelatin or a cast military explosive 
(composition B or pentolite) (fig. 11) is recommended. Cast 



primers have a sensitive inner core that will accept detonation 
from a detonator or detonating cord, but are quite insensitive 
to external shock or friction. Cast phmers are available which 
have built-in millisecond delay units (fig. 12). These primers, 
when strung on a single detonating cord downline, enable the 
blaster to place as many delayed decks in the blasthole as the 
blast design requires. 



13 



CAST PRIMER FOR 
DETONATING CORD 



CAST PRIMER FOR 
BLASTING CAP 




Hgure 11.— Cast primers for 
onating cord. 




Although small 1 -lb cast primers are popular, even in large 
boreholes, a primer functions best when its diameter is near 
that of the borehole. A two-stage primer, with a charge of 
high-energy dry blasting agent or slurry poured around a cast 
primer or ammonia gelatin, is frequently used in large-diameter 
blastholes. In Sweden, in small-diameter work, excellent results 
have been reported with a high-strength blasting cap used to 
initiate AN-FO, thus eliminating the need for a primer. In the 
United States, a more common practice in small-diameter 
work is to use a small primer designed to fit directly over a 
blasting cap, or a small cartridge of ammonia gelatin. More 
detailed priming recommendations are given in chapter 2. 

LIQUID OXYGEN EXPLOSIVE 
AND BLACK POWDER 

Liquid oxygen explosive (LOX) and black powder merit a 
brief mention because of their past importance. LOX consists 
of a cartridge of lampblack, carbon black, or charcoal, dipped 
into liquid oxygen just before loading. It derives its energy from 
the reaction of the carbon and oxygen to form carbon dioxide. 
LOX is fired with an ordinary detonator and attains velocities of 
12,000 to 19,000 fps. LOX, primarily used in U.S. strip coal 
mining, has been replaced by blasting agents, although it is 
still used in foreign countries. 




Figure 12. — Delay cast primer. (Courtesy Atlas Powder Co.) 



14 



Black powder, a mixture of potassium or sodium nitrate, 
charcoal, and sulfur, dates from ancient times. Once the principal 
commercial explosive, black powder is extremely prone to 
accidental initiation by flame or spark. When initiated, it undergoes 
buming at a very rapid rate. This rapid burning, called deflagration, 
is much slower than typical detonation velocities. Black powder 



has a specific gravity of 1 .6 or less, depending on granulation, 
has poor water resistance, and emits large volumes of noxious 
gases upon deflagration. Black powder finds limited use in 
blasting dimension stone where a minimum of shattering effect 
is desired. It is not an efficient explosive for fragmenting rock. 



PROPERTIES OF EXPLOSIVES 



Explosives and blasting agents are characterized by various 
properties that determine how they will function under field 
conditions. Properties of explosives which are particularly 
important to the blaster include "strength," detonation velocity, 
density, water resistance, fume class, detonation pressure, 
borehole pressure, and sensitivity and sensitiveness. Numerous 
other properties can be specified for explosives but have not 
been included here because of their lack of importance to the 
field blaster. 



1 . Using a larger charge diameter (see fig. 13, after Ash). 

2. Increasing density (although excessively high densities 
in blasting agents may seriously reduce sensitivity). 

3. Decreasing particle size (pneumatic injection of AN-FO 
in small diameter boreholes accomplishes this). 

4. Providing good confinement in the borehole. 



STRENGTH 

The strength of explosives has been expressed in various 
terms since the invention of dynamite. The terms "weight 
strength" and "cartridge strength," which originally indicated 
the percentage of nitroglycerin in an explosive, were useful 
when nitroglycerin was the principal energy-producing ingredient 
in explosives. However, with the development of products with 
decreasing proportions of nitroglycerin, these strength ratings 
have become misleading and inaccurate (4) and do not 
realistically compare the effectiveness of various explosives. 

More recently, calculated energy values have been used to 
compare the strengths of explosives with AN-FO being used 
as a base of 1 .0. Although this system has not been universally 
adopted, it is an improvement over weight strength and cartridge 
strength in estimating the work an explosive will do. Other 
strength rating systems such as seismic execution value, 
strain pulse measurement, cratering, and the ballistic mortar 
have been used, but do not give a satisfactory prediction of the 
field performance of an explosive. 

Undenwater tests have been used to determine the shock 
energy and expanding gas energy of an explosive. These two 
energy values have been used quite successfully by explosive 
manufacturers in predicting the capability of an explosive to 
break rock. 



DETONATION 
VELOCITY 

Detonation velocity is the speed at which the detonation 
front moves through a column of explosives. It ranges from 
about 5,500 to 25,000 fps for products used commercially 
today. A high detonation velocity gives the shattering action 
that many experts feel is necessary for difficult blasting conditions, 
whereas low-velocity products are normally adequate for the 
less demanding requirements typical of most blasting jobs. 
Detonation velocity, particularly in modern dry blasting agents 
and slurries, may vary considerably depending on field conditions. 
Detonation velocity can often be increased by the following 
(5): 



5. Providing a high coupling ratio (coupling ratio is the 
percentage of the borehole diameter filled with explosive). 

6. Using a larger initiator or primer (this will increase the 
velocity near the primer but will not alter the steady state 
velocity). 

There is a difference of opinion among experts as to how 
important detonation velocity is in the fragmentation process. 
It probably is of some benefit in propagating the initial cracks in 
hard, massive rock. In the softer, prefractured rocks typical of 
most operations, it is of little importance. 



DENSITY 

Density is normally expressed in terms of specific gravity, 
which is the ratio of the density of the explosive to that of water. 



20 



Cast 50-50 pentolite high explosive 

Straight gelatin, 60 pet high explosive 
Semigelatin.45pct bulk strength high explosive 




(water gel) blasting agent 



Premixed AN-FO 
blasting agent 



3 4 5 6 7 8 9 1 
CHARGE DIAMETER, in 

Figure 1 3.— Effect of charge diameter on detonation veiocity. 



15 



Figure 14. — Nomograph for finding loading density. 



A useful expression of density is loading density, which is the 
weight of explosive per unit length of charge at a specified 
diameter, commonly expressed in pounds perfect. Figure 14 
shows a nomograph for finding loading density. Cartridge 
count (number of IVa- by 8-in cartridges per 50-lb box) is 
useful when dealing with cartridged high explosives and is 
approximately equal to 1 41 divided by the specific gravity. The 
specific gravity of commercial products ranges from 0.5 to 1 .7 
The density of an explosive determines the weight that can 
be loaded into a given column of borehole. Where drilling is 
expensive, a higher cost, dense product is frequently justified. 
The energy per unit volume of explosive is actually a more 
important consideration, although it is not a commonly reported 
explosive property. 



WATER RESISTANCE 

Water resistance is the ability of an explosive product to 
withstand exposure to water without losing sensitivity or 
efficiency. Gelled products such as gelatin dynamites and 
water gels have good water resistance. Nongelatinized high 
explosives have poor-to-good water resistance. Ammonium 
nitrate prills have no water resistance and should not be used 
in the water-filled portions of a borehole. The emission of 
brown nitrogen oxide fumes from a blast often indicates inefficient 
detonation frequently caused by water deterioration, and signifies 
the need for a more water-resistant explosive or external 
protection from water in the form of a plastic sleeve or a 
waterproof cartridge. 



FUME CLASS 

Fume class is a measure of the amount of toxic gases, 
primarily carbon monoxide and oxides of nitrogen, produced 
by the detonation of an explosive. Most commercial blasting 
products are oxygen balanced both to minimize fumes and to 
optimize energy release per unit cost of ingredients. Fumes 
are an important consideration in tunnels, shafts, and other 
confined spaces. Certain blasting conditions may produce 
toxic fumes even with oxygen-balanced explosives. Insufficient 
charge diameter, inadequate priming or initiation, water 
deterioration, removal of wrappers, or the use of plastic borehole 
liners all increase the likelihood of generating toxic gases. 
Table 2 shows fume classes adopted by the Institute of Makers 
of Explosives (7). MSHA standards limit the volume of poisonous 
gases produced by a permissible explosive to 2.5 cu ft/lb of 
explosive. 



Table 2. - Fume classes designated by the 
institute of Makers of Explosives 

(Bichel gage method) 

Cubic foot of poisonous gases 
Fume class per 200 g of explosive 

1 0.16 

2 0.16- .33 

3 .33- .67 



16 



DETONATION PRESSURE 

The detonation pressure of an explosive is primarily a function 
of the detonation velocity squared times the density. It is the 
head-on pressure of the detonation wave propagating through 
the explosive column, measured at the C-J plane (fig. 2). 
Although the relationship of detonation velocity and density to 
detonation pressure is somewhat complex, and depends on 
the ingredients of an explosive, the following approximation is 
one of several that can be made (4): 

P = 4.18 X 10^ DC^ / (1 + 0.8 D), 

where P = detonation pressure, in kilobars, (1 kb = 14,504 
psi), 
D = specific gravity, 
and C = detonation velocity, in feet per second. 

The nomograph in figure 15, based on this formula, can be 
used to approximate the detonation pressure of an explosive 



Detonation 
velocity, 

10^ fps 



25 



20 



15 



10 



Detonation 

pressure, 

kb 



300- 

200- 
150- 

100- 



50- 
40 

30 

20 

15 

10- 



Specific 
gravity 

1.6-^ 
1.3-E 
1.0-5 
.8 — 



Figure 15.— Nomograph for finding detonation pressure. 



when the detonation velocity and specific gravity are known. 
Some authorities feel that a high detonation pressure resulting 
in a strong shock wave is of major importance in breaking very 
dense, competent rock. Others, including Swedish experts (8) 
feel that it is of little or no importance. As a general 
recommendation, in hard, massive rock, if the explosive being 
used is not giving adequate breakage, a higher velocity explosive 
(hence, a higher detonation pressure explosive) may alleviate 
the problem. Detonation pressures for commercial products 
range from about 5 to over 150 kb. 



BOREHOLE PRESSURE 

Borehole pressure, sometimes called explosion pressure, 
is the pressure exerted on the borehole walls by the expanding 
gases of detonation after the chemical reaction has been 
completed. Borehole pressure is a function of confinement 
and the quantity and temperature of the gases of detonation. 
Borehole pressure is generally considered to play the dominant 
role in breaking most rocks and in displacing all types of rocks 
encountered in blasting. This accounts for the success of 
AN-FO and aluminized products which yield low detonation 
pressures but relatively high borehole pressures. The 100 
pet coupling obtained with these products also contributes to 
their success. Borehole pressures for commercial products 
range from less than 1 to 60 kb or more. Borehole pressures 
are calculated from hydrodynamic computer codes or 
approximated from undenvater test results, since borehole 
pressure cannot be measured directly. Many AN-FO mixtures 
have tjorehole pressures largerthan their detonation pressures. 
In most high explosives the detonation pressure is the greater. 

A Swedish formula (8) for comparing the relative rock-breaking 
capability of explosives is 

S = 1/6(V^A/j + 5/6(0/0 J, 

where S is the strength of the explosive, V is the reaction 
product gas volume, Q is the heat energy, the subscript x 
denotes the explosive being rated, and the subscript o denotes 
a standard explosive. This corresponds closely to the borehole 
pressure of an explosive. Although the complexity of the 
fragmentation process precludes the use of a single property 
for rating explosives, more and more explosives engineers are 
relying on borehole pressure as the single most important 
descriptor in evaluating an explosive's rock-breaking capability. 



SENSITIVITY AND 
SENSITIVENESS 

These are two closely related properties that have become 
increasingly important with the advent of dry blasting agents 
and slurries, which are less sensitive than dynamites. Sensitivity 
is defined as an explosive's susceptibility to initiation. Sensitivity 
to a No. 8 test blasting cap, under certain test conditions, 
means that a product is classified as an explosive. Lack of cap 
sensitivity results in a classification as a blasting agent. Sensitivity 
among different types of blasting agents varies considerably 
and is dependent upon ingredients, particle size, density, 
charge diameter, confinement, the presence of water, and 
often, particularly with slurries, temperature (2). Manufacturers 
often specify a minimum recommended primer for their products, 
based on field data. In general, products that require larger 
primers are less susceptible to accidental initiation and are 
safer to handle. 

Sensitiveness is the capability of an explosive to propagate 



17 



a detonation once it has been initiated. Extremely sensitive 
explosives, under some conditions, may propagate from hole 
to hole. An insensitive explosive may fail to propagate throughout 
its charge length if its diameter is too small. Sensitiveness is 



closely related to critical diameter, which is the smallest diameter 
at which an explosive will propagate a stable detonation. 
Manufacturers' technical data sheets give recommended 
minimum diameters for individual explosives. 



EXPLOSSVE SELECTION CRITERIA 



Proper selection of the explosive is an important part of blast 
design needed to assure a successful blasting program (6). 
Explosive selection is dictated by economic considerations 
and field conditions. The blaster should select a product that 
will give the lowest cost per unit of rock broken, while assuring 
that fragmentation and displacement of the rock are adequate 
for the job at hand. Factors which should be taken into 
consideration in the selection of an explosive include explosive 
cost, charge diameter, cost of drilling, fragmentation difficulties, 
water conditions, adequacy of ventilation, atmospheric 
temperature, propagating ground, storage considerations, 
sensitivity considerations, and explosive atmospheres. 



EXPLOSIVE COST 

No other explosive product can compete with AN-FO on the 
basis of cost per unit of energy. Both of the ingredients, 
ammonium nitrate and fuel oil, are relatively inexpensive, both 



participate fully in the detonation reaction, and the manufacturing 
process consists of simply mixing a solid and a liquid ingredient 
(fig. 16). The safety and ease of storage, handling, and bulk 
loading add to the attractive economics of AN-FO. It is because 
ofthese economics that AN-FO now accounts for approximately 
80 pet, by weight, of all the explosives used in the United 
States. By the pound, slurry costs range from slightly more 
than AN-FO to about four times the cost of AN-FO. The cheaper 
slurries are designed for use in large-diameter blastholes and 
contain no high-cost, high-energy ingredients. They are relatively 
low in energy per pound. The more expensive slurries are (1) 
those designed to be used in small diameters and (2) high- 
energy products containing large amounts of aluminum or 
other high-energy ingredients. Dynamite cost ranges from 
four to six times that of AN-FO, depending largely on the 
proportion of nitroglycerin or other explosive oil. 

Despite its excellent economics, AN-FO is not always the 
best product for the job, because it has several shortcomings. 
AN-FO has no water resistance, it has a low specific gravity. 




Figure 16.— Field mixing of AN-FO, (Courtesy Hercules inc.) 



18 



and under adverse field conditions it tends to detonate 
inefficiently. Following are additional factors that should be 
taken into account when selecting an explosive. 



CHARGE DIAMETER 

The dependability and efficiency of AN-FO are sometimes 
reduced at smaller charge diameters, especially in damp 
conditions or with inadequate confinement. In diameters under 
2 in, AN-FO functions best when pneumatically loaded into a 
dry blasthole. When using charge diameters smaller than 2 in, 
many blasters prefer the greater dependability of a cartridged 
slurry or dynamite despite the higher cost. The cost saving that 
AN-FO offers can be lost through one bad blast. 

At intermediate charge diameters, between 2 and 4 in, the 
use of dynamite is seldom justified because AN-FO and slurries 
function quite well at these diameters. Slurries designed for 
use in intermediate charge diameters are somewhat cheaper 
than small-diameter slurries and are more economical than 
dynamite. The performance of AN-FO in a 4-in-diameter blasthole 
is substantially better than at 2 in. Where practical, bulk loading 
in intermediate charge diameters offers attractive economics. 

In blasthole diameters larger than 4 in, a bulk-loaded AN-FO 
or slurry should be used unless there is some compelling 
reason to use a cartridged product. AN-FO's efficiency and 
dependability increase as the charge diameter increases. 
Where the use of a slurry is indicated, low-cost varieties func- 
tion well in large charge diameters. 



velocity in rock fragmentation, there is evidence tnat a high 
velocity does help in fragmenting hard, massive rock (10). 
With cartridged dynamites, the detonation velocity increases 
as the nitroglycerin content increases, with gelatin dynamites 
having higher velocities than their granular counterparts. Several 
varieties of sluny , and particularly emulsions, have high velocities. 
The individual manufacturer should be consulted for a 
recommendation on a high-velocity product. In general, 
emulsions exhibit higher velocities than water gels. 

The detonation velocity of AN-FO is highly dependent on its 
charge diameter and particle size. In diameters of 9 in or 
greater, AN-FO's detonation velocity will normally exceed 1 3,000 
fps, peaking near 1 5,000 fps in a 1 5-in diameter. These velocities 
compare favorably with velocities of most other explosive 
products. In smaller diameters the detonation velocity falls off, 
until at diameters below 2 in the velocity is less than half the 
15,000-fps maximum. In these small diameters, the velocity 
may be increased to nearly 1 0,000 fps by high velocity pneumatic 
loading, which pulverizes the AN-FO and gives it a higher 
loading density. As a cautionary note, pressures higher than 
30 psi should never be used with a pressure vessel pneumatic 
loader. Full line pressures of 90 to 1 10 psi are satisfactory for 
ejectors. In many operations with expensive drilling and difficult 
fragmentation, it may be advantageous for the blaster to 
compromise and use a dense, high-velocity explosive in the 
lower position of the borehole and AN-FO as a top load. 



WATER CONDITIONS 



COST OF DRILLING 

Under normal drilling conditions, the blaster should select 
the lowest cost explosive that will give adequate, dependable 
fragmentation. However, when drilling costs increase, typically 
in hard, dense rock, the cost of explosive and the cost of 
drilling should be optimized through controlled, in-the-mine 
experimentation with careful cost analysis. Where drilling is 
expensive, the blaster will want to increase the energy density 
of the explosive, even though explosives with high-energy 
densities tend to be more expensive. Where dynamites are 
used, gelatin dynamites will give higher energy densities than 
granular dynamites. The energy density of a slurry depends 
on its density and the proportion of high-energy ingredients, 
such as aluminum, used in its formulation. Because of the 
diverse varieties of slurries on the market, the individual 
manufacturer should be consulted for a recommendation on a 
high-energy slurry. 

In small-diameter blastholes, the density of AN-FO may be 
increased by up to 20 pet by high-velocity pneumatic loading. 
The loading density (weight per foot of borehole) of densified 
AN-FO cartridges is about the same as that of bulk AN-FO 
because of the void space between the cartridge and the 
borehole wall. The energy density of AN-FO can be increased 
by the addition of finely divided aluminum. The economics of 
aluminized AN-FO improve where the rock is more difficult to 
drill and blast. 



AN-FO has no water resistance. It may, however, be used in 
blastholes containing water if one of two techniques is followed. 
First, the AN-FO may be packaged in a water-resistant, 
polyburlap container. To enable the AN-FO cartridge to sink in 
water, part of the prills are pulverized and the mixture is 
vibrated to a density of about 1.1 g/cu cm. Of course, if a 
cartridge is ruptured during the loading process, the AN-FO 
will quickly become desensitized. In the second technique, the 
blasthole is dewatered by using a down-the-hole submersible 
pump (3). A waterproof liner is then placed into the blasthole 
and AN-FO is loaded inside the liner before the water reenters 
the hole. Again, the AN-FO will quickly become desensitized if 
the borehole liner is ruptured. The appearance of orange- 
brown nitrogen oxide fumes upon detonation is a sign of water 
deterioration, and an indication that a more water-resistant 
product or better external protection should be used. 

Slurries are gelled and cross-linked to provide a barrier 
against water intrusion, and as a result, exhibit excellent water 
resistance. The manufacturer will usually specify the degree 
of water resistance of a specific product. When dynamites are 
used in wet holes, gelatinous varieties are preferred. Although 
some granular dynamites have fair water resistance, the slightly 
higher cost of gelatins is more than justified by their increased 
reliability in wet blast 'les. 



ADEQUACY 
OF VENTILATION 



FRAGMENTATION 
DIFFICULTIES 

Expensive drilling and fragmentation difficulties frequently 
go hand in hand because hard, dense rock may cause both. 
Despite the controversy as to the importance of detonation 



Although most explosives are oxygen-balanced to maximize 
energy and minimize toxic detonation gases, some are inherently 
"dirty" from the standpoint of fumes. Even with oxygen-balanced 
products, unfavorable field conditions may increase the 
generation of toxic fumes, particularly when explosives without 
water resistance get wet. The use of plastic borehole liners, 
inadequate charge diameters, removal of a cartridged explosive 



19 



from its wrapper, inadequate priming, or an improper explosive 
ingredient mix may cause excessive fumes. 

In areas where efficient evacuation of detonation gases 
cannot be assured (normally underground), AN-FO should be 
used only in absolutely dry conditions. Most small-diameter 
slurries have very good fume qualities. Large-diameter slurries 
have variable fume qualitities. The manufacturer should be 
consulted for a recommendation where fume control is important. 
Of the cartridged dynamites, ammonia gelatins and semigelatins 
have the best fume qualities. High-density ammonia dynamites 
are rated good, low-density ammonia dynamites are fair, and 
straight dynamites are poor, as shown in table 1 . In permissible 
blasting, where fumes are a concern, care should be exercised 
in selecting the explosives because many permissibles have 
poor fume ratings. Permissibles with good fume ratings are 
available. 



ATMOSPHERIC TEMPERATURE 

Until the development of slurries, atmospheric temperatures 
were not an important factor in selecting an explosive. For 
many years, dynamites have employed low-freezing explosive 
oils which permits their use in the lowest temperatures 
encountered in the United States. AN-FO and slurries are not 
seriously affected by low temperatures if priming is adequate. 
A potential problem exists with slurries that are designed to be 
cap sensitive. At low temperatures, many of these products 
may lose their cap sensitivity, although they will still function 
well if adequately primed. If a slurry is to be used in cold 
weather the manufacturer should be asked about the temperature 
limitation on the product. 

The effect of temperature is alleviated if explosives are 
stored in a heated magazine or if they are in the borehole long 
enough to achieve the ambient borehole temperature. Except 
in permafrost or in extremely cold weather, borehole 
temperatures are seldom low enough to render slurries 
insensitive. 



PROPAGATING 
GROUND 

Propagation is the transfer or movement of a detonation 
from one point to another. Although propagation normally 
occurs within an explosive column, it may occur between 
adjacent blastholes through the ground. In ditch blasting, a 
very sensitive straight nitroglycerin dynamite is sometime used 
to purposely accomplish propagation through the ground. This 
saves the cost of putting a detonator into each blasthole. 
Propagation ditch blasting works best in soft, water-saturated 
ground. 

In all other types of blasting, propagation between holes is 
undesirable t)ecause it negates the effect of delays. Propagation 
between holes will result in poor fragmentation, failure of a 
round to pull properly, and excessive ground vibrations, airblast, 
and flyrock. In underground blasting, the entire round may fail 
to pull. The problem is most serious when using small blastholes 
loaded with dynamite. Small blastholes require small burdens 
arxl spacings, increasing the chance of hole-to-hole propagation, 
particularly when sensitive explosives are used. Water saturated 
material and blasthole deviation compound the problem. When 
propagation is suspected, owing to poor fragmentation, violent 
shots, or high levels of ground vibrations, the use of a less 
sensitive product usually solves the problem. Straight 
nitroglycerin dyn£imrte is the nnost sensitive commercial explosive 



available, followed by other granular dynamites, gelatin 
dynamites, cap-sensitive slurries, and blasting agents, in 
decreasing order of sensitivity. 

A different problem can occur when AN-FO or slurry blasting 
agents are used at close spacings in soft ground. The shock 
from an adjacent charge may dead press a blasting agent 
column and cause it to misfire. 



STORAGE 
CONSIDERATIONS 

Federal requirements for magazine construction are less 
stringent for blasting agents than for high explosives (13). 
Magazines for the storage of high explosives must be well 
ventilated and must be resistant to bullets, fire, weather, and 
theft; whereas a blasting agent magazine need only be theft 
resistant. Although this is not an overriding reason for selecting 
a blasting agent rather than an explosive, it is an additional 
point in favor of blasting agents. 

Some activities such as powerline installation and light 
construction require the periodic use of very small amounts of 
explosives. In this type of work the operator can advantageously 
use two-component explosives. Two-component explosives 
are sold as separate ingredients, neither of which is explosive. 
The two components are mixed at the jobsite as needed, and 
the mixture is considered a high explosive. Persons who mix 
two-component explosives are often required to have a 
manufacturer's license. 

Federal regulations do not require ingredients of two- 
component explosives to be stored in magazines nor is there a 
minimum distance requirement for separation of the ingredients 
from each other or from explosive products. Even though 
there is no Federal regulation requiring magazine storage, 
two-component explosives should be protected from theft. 
Two-component explosives stored underthe jurisdiction of the 
U.S. Forest Service must be stored in magazines. 

The use of two-component explosives eliminates the need 
for frequent trips to a magazine. However, when large amounts 
of explosives are used, the higher cost and the time-consuming 
process of explosive mixing begin to outweigh the savings in 
traveltime. 

SENSITIVITY 
CONSIDERATIONS 

Sensitivity considerations address questions of the safety 
gind the dependability of an explosive. More sensitive explosives 
such as dynamites are somewhat more vulnerable to accidental 
initiation by impact or spark than blasting agents. Slurries and 
nitrostarch-based explosives are generally less sensitive to 
impact than nitroglycerin-based dynamites. However, more 
sensitive explosives, all conditions being equal, are less likely 
to misfire in the blasthole. For instance, upon accidental impact 
from a drill bit, a blasting agent is less likely to detonate than a 
dynamite. This does not mean that the blasting agent will not 
detonate when accidentally impacted. Conversely, under adverse 
situations such as charge separation in the blasthole, very 
small charge diameters, or low temperatures, dynamites are 
less likely to misfire than blasting agents. This tradeoff must be 
considered primarily when selecting an explosive for small- 
diameter work. Other selection criteria usually dictate the use 
of blasting agents when the blasthole diameter is large. 

It can be concluded from 1981 explosive consumption figures 
(12) and field observations that most of the dynamite still used 
in this country is used in construction, small quarries, and 



20 



underground mines, where many operators consider a more 
sensitive explosive beneficial in their small-diameter blasting. 
When safely handled and properly loaded, dynamites, dry 
blasting agents, and slurries all have a place in small-diameter 
blasting. 



EXPLOSIVE ATMOSPHERES 

Blasting in a gassy atmosphere can be catastrophic if the 
atmosphere is ignited by the flame from the explosive. All 
underground coal mines are classified as gassy; some metal- 
nonmetal mines may contain methane or other explosive gases; 
and many construction projects encounter methane. Where 
gassy conditions are suspected, MSHA or OSHA should be 
consulted for guidance. 



Permissible explosives (14) offer protection against gas 
explosions. Most permissible explosives are relatively weak 
explosives, and will not do an adequate job in most rock, 
although some relatively powerful permissible gelatins, 
emulsions, and slurries are available. 

All underground coal mines are classified as gassy by MSHA, 
and permissible explosives are the only type of explosives that 
can be used in these mines without a variance from MSHA. 
Salt, limestone, uranium, potash, copper, trona, and oil shale 
mines may contain methane or other explosive gases and 
may be classified gassy on an individual basis by MSHA. In 
these gassy metal-nonmetal mines, MSHA may permit the 
use of nonpermissible products such as AN-FO, detonating 
cord, and certain other high explosives and blasting agents. 
These mines are required to operate under modified permissible 
rules developed by MSHA on a mine-by-mine basis. 



REFERENCES 



1 . Cook, M. A. Explosives— A Survey of Technical Advances. Ind. 
and Eng. Chem., v. 60, No. 7, July 1968, pp. 44-55. 

2. Damon, G. H., C. M. Mason, N. E. Hanna, and D. R. Forshey. 
Safety Recommendations for Ammonium Nitrate-Based Blasting Agents. 
BuMines IC 8746, 1977, 31 pp. 

3. Dannenberg, J. Blasthole Dewatering Cuts Costs. Rock Products, 
v. 76, No. 12, December 1973, pp. 66-68. 

4. Dick, R. A. Factors in Selecting and Applying Commercial 
Explosives and Blasting Agents. BuMines IC 8405, 1968, 30 pp. 

5. . The Impact of Blasting Agents and Slurries on 

Explosives Technology. BuMines IC 8560, 1972, 44 pp. 

6. Drury, F., and D. G. Westmaas. Considerations Affecting the 
Selection and Use of Modern Chemical Explosives. Proc. 4th Conf . on 
Explosives and Blasting Technique, New Orleans, LA, Feb. 1-3, 1978. 
Society of Explosives Engineers, Montville, OH, pp. 128-153. 

7. E. I. du Pont de Nemours & Co., Inc. (Wilmington, DE). Blaster's 
Handbook. 16th ed., 1978, 494 pp. 

8. Johansson, C. H., and U. Langefors. Methods of Physical 
Characterization of Explosives. Proc. 36th Interna'. Cong, of Ind. 



Chem., Brussels, v. 3, 1966, p. 610.; available for consultation at 
Bureau of Mines Twin Cities Research Center, Minneapolis, MN. 

9. Monsanto Co. (St. Louis, MO). Monsanto Blasting Products 
AN-FO Manual. Its Explosive Properties and Field Performance 
Characteristics. September 1 972, 37 pp. 

1 0. Porter, D. D. Use of Fragmentation To Evaluate Explosives for 
Blasting. Min. Cong. J., v. 60, No. 1, January 1974, pp. 41-43. 

1 1 . Robinson, R. V. Water Gel Explosives— Three Generations. 
Canadian Min. and Met. Bull., v. 62, No. 692, December 1969, pp. 
1317-1325. 

12. U.S. Bureau of Mines. Apparent Consumption of Industrial 
Explosives and Blasting Agents in the United States, 1981. Mineral 
Industry Survey, June 23, 1982, 12 pp. 

13. U.S. Department of the Treasury; Bureau of Alcohol, Tobacco, 
and Firearms. Explosive Materials Regulations. Federal Register, v. 
42, Nov. 149, Aug. 3, 1977, pp. 39316-39327; Federal Register, v. 45, 
No. 224, Nov. 18, 1980, pp. 76191-76209. 

14. U.S. Mine Enforcement and Safety Administration. Active List 
of Permissible Explosives and Blasting Devices Approved Before 
Dec. 31, 1975. MESA Inf. Rep. 1046, 1976, 10 pp. 



21 



Chapter 2.— INITIATION AND PRIMING 



iNITIATION SYSTEMS 



A considerable amount of energy is required to initiate a 
high explosive such as a dynamite or cap-sensitive slurry. In 
blasting, high explosives are initiated by a detonator, which is 
a capsule containing a series of relatively sensitive explosives 
that can be readily initiated by an outside energy source. 
Blasting agents, which are the most common products used 
as the main column charge in the blasthole, are even less 
sensitive to initiation than high explosives. To assure dependable 
initiation of these products, the initiator is usually placed into a 
container of high explosives, which in turn is placed into the 
column of blasting agent. 

An initiation system consists of three basic parts. 

1 . An initial energy source. 

2. An energy distribution network that conveys energy into 
the individual blastholes. 

3. An in-the-hole component that uses energy from the 
distribution network to initiate a cap-sensitive explosive. 

The initial energy source may be electrical, such as a generator 
or condenser-discharge blasting machine or a powerline used 
to energize an electric blasting cap, or a heat source such as a 
spark generator or a match. The energy conveyed to and into 
the individual blastholes may be electricity, a burning fuse, a 
high-energy explosive detonation, or a low-energy dust or gas 
detonation. Figure 17 shows a typical detonator or "business 
end" of the initiation system. This detonator, when inserted 
into a cap-sensitive explosive and activated, will initiate the 
detonation of the explosive column. Commercial detonators 
vary in strength from No. 6 to No. 1 2. Although No. 6 and No. 8 
detonators are the most common, there is a trend toward 
higher strength detonators, particularly when blasting with 
cap-sensitive products which are less sensitive than dynamites. 

The primer is the unit of cap-sensitive explosive containing 
the detonator. Where the main blasthole charge is high explosive, 
the detonator may be inserted into the column at any point. 
However, most of the products used for blasting today (blasting 
agents) are insensitive to a No. 8 detonator. To detonate these 
products, the detonator must be inserted into a unit of cap- 
sensitive explosive, which in turn is inserted into the blasting 
agent column at the desired point of initiation. 

The discussions of the various initiation and priming systems 
will concentrate primarily on common practice. With each 
system there are optional techniques and "tricks of the trade" 
that increase system versatility. It is a good idea to confer with 
the manufacturer before finalizing your initiation and priming 
program, so you fully understand how to best use a specific 
system. 



--:: 



) 



Energy 
input 




Crimp 



Ignition 
compound 



Priming 
charge 




Figure 17.— Instantaneous detonator. 



DELAY SERIES 



Figure 1 7 shows an instantaneous detonator. In this type of 
detonator, the base charge detonates within a millisecond or 
two after the external energy enters the detonator. However, 



in most types of blasting, time intervals are required between 
the detonation of various blastholes or even between decks 
within a blasthole. To accomplish this, a delay element containing 



22 



Energy 
input 




Crimp 



Delay 
powder 



Priming 
charge 



Base 
charge 



Figure 18. — Delay detonator. 



a burning powder is placed immediately before the priming 
charge in the detonator. Figure 1 8 shows a delay detonator. 

There are three basic delay senes; slow or tunnel delays, 
fast or millisecond delays, and coal mine delays for use in 
underground coal mines. For all commercial delay detonators, 
the delay time is determined by the length and burning rate of 
the delay powder column. As a result, slow delay caps may be 
quite long in dimension whereas lower period millisecond 
delays are shorter. Although the timing of delay detonators is 
sufficiently accurate for most blasting needs, these delays are 
not precise, as indicated by recent research. Recently, however, 
manufacturers' tolerances for some delay caps have been 
tightened. It is important to use the manufacturer's recommended 
current level to initiate electric blasting caps. Current levels 
above or below the recommended firing level can further 
increase the scatter in delay cap firing times. Extremely high 
currents can speed up delay firing times. Near the minimum 
firing current, delays can become extremely erratic. 

Slow delays are useful underground under tight shooting 
conditions where it is essential that the burden on one hole 
moves before a subsequent hole fires. This situation may 
occur in tunnels, shafts, underground metal-nonmetal mines, 
and in trenching. Slow delays are available with all initiation 
systems except surface detonating cord and delay cast primers. 
Delay intervals are typically 0.5 to 1 sec. 

Millisecond delays are the most commonly used delays and 
are useful wherever the tight conditions previously mentioned 
are not present. Millisecond delays provide improved 
fragmentation, controlled throw, and reduced ground vibration 
and airblast, as compared with simultaneous firing. They are 
available with all initiation systems. In millisecond detonators, 
delay intervals are 25 to 50 ms in the lower periods and are 
longer in the higher periods. In detonating cord delay connec- 
tors, the delay may be as short as 5 ms. 

Coal mine delays are a special series of millisecond delays. 
Since only electric initiation systems are permissible in 
underground coal mines, coal mine delays are available only 
with electric initiators. Delay intervals are from 50 to 100 ms, 
with instantaneous caps being prohibited. Coal mine delay 
caps always utilize copper alloy shells and iron leg wires. Iron 
leg wires are also available optionally with ordinary electric 
detonators and are used primarily to facilitate magnetic removal 
of the wires from the muck pile, such as in trona and salt 
mines. 



ELECTRIC INITIATION 



Electric initiation has been used for many years in both 
surface and underground blasting. An electric blasting cap 
(fig. 1 9) consists of two insulated leg wires that pass through a 



waterproof seal and into a metal capsule containing a series of 
explosive powders (fig. 20). Leg wires of various lengths are 
available to accommodate various borehole depths. Inside the 



23 




Figure 19. — Electric blasting caps. (Courtesy Du Pont Co.) 




Crimps 



Bridge wire 



Ignition charge 



Delay element 



Primer charge 



Base charge 



Figure 20. — Delay electric blasting cap. 



capsule the two leg wires are connected by a fine filament 
bridge wire embedded in a highly heat-sensitive explosive. 
Upon application of electric current the bridge wire heats 
sufficiently to initiate the ignition mixture, which in turn initiates 
a series of less sensitive, more powerful explosives. Detonators 
are available in strengths ranging from about No. 6 to No. 12, 
with No. 6 and No. 8 being most common. Trends recently are 
toward higher strength detonators. 

Most electric blasting caps have copper leg wires. Iron leg 
wires are available for use where magnetic separation is used 
to remove the leg wires at the preparation plant. Atlas Powder^ 
Co. has prepared an excellent handbook that describes electric 
blasting procedures in detail0.^ 

The Saf-T-Det and Magnadet electric blasting caps are two 
recent developments. The Saf-T-Det resembles a standard 
electric blasting cap but has no base charge. A length of 
1 00-gr or less detonating cord is inserted into a well to act as a 
base charge just before the primer is made up. The device is 
similar to an electric blasting cap in regard to required firing 
currents and extraneous electricity hazards. The Saf-T-Det is 
manufactured in India and is not available in the United States 
at this time. 

The Magnadet is also similar to a standard electhc blasting 
cap, except that the end of each cap lead contains a plastic- 
covered ferrite toroidal ring. The system is hooked up by 
passing a single wire through each ring. A special blasting 
machine is used to fire these detonators. The manufacturer, 
ICI of Scotland, claims ease of hookup and protection against 
extraneous electricity as advantages of this system. 



TYPES OF CIRCUITS 

In order to fire electric blasting caps, the caps must be 
connected into circuits and energized by a power source. 
There are three types of electric blasting circuits (fig. 21). In 
order of preference they are series, parallel series, and parallel. 



Reference to specific trade names or manufacturers does not imply endorsement 
by tfie Bureau of Mines. 

^Italicized numbers in parentheses refer to items in the list of references at the 
end of this chapter. 



24 



Electric blasting 
caps 




Electric blosting 
caps 



Bus wires 

Electric blasting 



Figure 21 .—Types of electric biasling circuits. 



In series circuits all the caps are connected consecutively so 
that the current from the power source has only one path to 
follow. The series circuit is recommended because of its 
simplicity. Also, all the caps receive the same amount of 
current. 

Figure 22 shows recommended wire splices for blasting 
circuits. To splice two small wires, the wires are looped and 
twisted together. To connect a small wire to a large wire, the 
small wire is wrapped around the large wire. 

The electrical resistance of a series of caps is equal to the 
sum of the resistances of the individual caps. For most blasting 
machines, it is recommended that the number of caps in a 
single series be limited to 40 to 50, depending on the leg wire 



LIGHT GAGE TO HE a 




Figure 22.— Recommended wire splices. 



length. Longer leg wires require smaller series. The limit for 
most small twist-type blasting machines is 10 caps with 30-ft 
leg wires. 

Many blasters minimize excess wire between holes to keep 
the blast site from being cluttered. The ends of the cap series 
are extended to a point of safety by connecting wire, which is 
usually 20 gage, but should be heavier where circuit resistance 
is a problem or when using parallel circuits. This connecting 
wire is considered expendable and should be used only once. 
The connecting wire is in turn connected to the firing line, 
which in turn is connected to the power source. 

The firing line contains two single conducting wires of 12 
gage or heavier, and is reused from shot to shot. It may be on a 
reel mechanism for portability, or may be installed along the 
wall of a tunnel in an underground operation. Installed firing 
lines should not be grounded, should be made of copper 
rather than aluminum, and should have a 15-ft lightning gap 
near the power source to guard against premature blasts. The 
firing line should be inspected frequently and replaced when 
necessary. 

When the number of caps in a round exceeds 40 to 50, the 
parallel series circuit is recommended. In a parallel series 
circuit, the caps are divided into a number of individual series. 
Each series should contain the same number of caps or the 
same resistance to assure even current distribution. The leg 
wires of the caps in each series are connected consecutively. 
Next, two bus wires, as shown in figure 21 , are placed in such 
a position that each end of each series can be connected as 
shown in the figure. The bus wire is usually about 14 gage or 
heavier and may be either bare or insulated. Where bare wires 
are used, care must be exercised to prevent excessive current 
leakage to the ground. It is recommended that insulated bus 
wires be used and that the insulation be cut away at point of 
connection with the blasting cap series. To assure equal current 
distribution to each series, one bus wire should be reversed as 
shown in figure 21. With parallel series circuits, 14 gage or 
heavier gage connecting wire is used to reduce the total circuit 
resistance. 

The third type of blasting circuit is the straight parallel circuit. 
The straight parallel circuit is less desirable to use than the 
series or series parallel circuits for two reasons. First, its 
nature is such that it cannot be checked. Broken leg wires or 
faulty connections cannot be detected once the circuit has 
been hooked up. Second, because the available current is 
divided by the number of caps in the circuit, powerline firing 
must often be used to provide adequate current for large 
parallel circuits. The problems associated with powerline firing 
will be discussed later. 

Parallel circuits are not appropriate for surface blasting but 
they are used to some extent for tunnel blasting. Parallel 
circuits are similar to parallel series except that instead of each 
end of a series circuit being connected to alternate bus wires, 
each leg wire of each cap is connected directly to the bus 
wires, as shown in figure 21. In underground blasts using 
parallel circuits, bare bus wire is usually strung on wooden 
pegs driven into the face to avoid grounding. As with parallel 
series circuits, the bus wires are reversed as shown in figure 
21. 

In a parallel circuit the lead wire (firing line) represents the 
largest resistance in the circuit. Keeping the lead wire as short 
as possible, consistent with safety, is the key to firing large 
numbers of caps with parallel circuits. Doubling the length of 
the lead wire reduces the number of caps that can be fired by 
almost half. Heavy (12 to 14 gage) bus wires are used to 
reduce the resistance. A 1 4-gage connecting wire, rather than 
a lighter gage, is recommended to reduce the circuit resistance. 



25 



CIRCUIT 
CALCULATIONS 

Only the very basics of circuit calculations are covered here. 
For more detail on circuit calculations or other of the many 
Intricacies of electrical blasting the reader should refer to a 
detailed electric blasting handbook such as reference 2. Figure 
23 shows the resistance calculations for cap circuits for series, 
parallel series, and straight parallel circuits. 

The resistance of a series circuit is the easiest to calculate. 
First, the resistance of a single cap, as specified by the 
manufacturer, is multiplied by the number of caps to determine 
the resistance of the cap circuit. To this is added the resistance 
of the connecting wire and that of the firing line to determine 
the resistance of the total circuit. Since the firing line contains 
two wires, there will be 2 ft of wire for every foot of firing line. 
Where bus wire is used (parallel or parallel series circuits) the 
resistance of one-half of the length of the bus wire is added to 
find the total circuit resistance. When firing from a powerline, 
the voltage of the line divided by the resistance of the circuit 
will give the current flow. In a single series circuit, all of this 
current flows through each cap. The minimum recommended 
firing current per cap is 1 .5 amp dc or 2.0 amp ac. The current 
output of condenser (capacitor) discharge blasting machines 
may vary with the circuit resistance, but not linearly. 
Manufacturer's specifications must be consulted to determine 
the amperage of a specific machine across a given resistance. 
For a generator blasting machine, the manufacturer rates the 
machine in terms of the number of caps it can fire. 



SIMPLE SERIES 



• 


I 

:Rc 

:Rc Rt=nrc 

;Rc 




PARALLE 


L SERIES 




Jrc : 
|rc : 


: r, 1 I.I.I 

:Rc If N|=N2 = N3, 

IRc '►'-Rt=Rc-^. 




PAR/1 


LLEL 


' |rc 


J. < 



KEY 

Rj Total resistance , 

Rc Resistance of I cop 

N Nunnber of caps 

N3 Number of series 

N|_2,3 Number of cops in a series 

Figure 23.— Calculation of cap circuit resistance. 



The resistance calculation for a parallel series circuit is as 
follows. First the resistance of each cap series is calculated as 
previously described. Remember, in a good parallel series 
circuit the resistance of each series should be equal. The 
resistance of a single series is then divided by the number of 
series to find the resistance of the cap circuit. To this are 
added the resistance of half the length of bus wire used, the 
resistance of the connecting wire, and the resistance of the 
firing line, to obtain the total circuit resistance. The locations of 
the bus wire, connecting wire, and firing line are shown in 
figure 21 . The current flow is determined either by dividing the 
powerline voltage by the circuit resistance or in the case of a 
condenser discharge machine, by checking the manufacturer's 
specifications. The current flow is divided by the number of 
series to determine the current^flow through each series. 

For straight parallel circuTts, the resistance of the cap circuit 
is equal to the resistance of a single cap divided by the number 
of caps. As can readily be seen, this is usually a very small 
value. For 20 short leg wire caps, the resistance is less than 
0.1 ohm. The resistance of the connecting wire, the firing line, 
and one-half the bus wire are added to find the total resistance. 
The current flow is determined in the same manner as with 
series and parallel series circuits. The current flow is divided 
by the number of caps to determine the current flow through 
each cap. 



POWER SOURCES 

Electric blasting circuits can be energized by generator-type 
blasting machines, condenser-discharge blasting machines, 
and powerlines. Storage and dry cell batteries are definitely 
not recommended for blasting because they cannot be depended 
on for a consistent output. 

Generator blasting machines may be of the rack-bar (push 
down) or the key-twist type. The capacity of rack-bar machines 
ranges from 30 to 50 caps in a single series, while key-twist 
machines will normally initiate 1 or 20 caps in a single sehes. 
The actual current put out by these machines depends on the 
condition of the machine and the effort exerted by the shot- 
firer. When using a rack-bar machine, the terminals should be 
on the opposite side of the machine from the operator. Both 
the rack-bar and twist machines should be operated vigorously 
to the end of the stroke because the current flows only at the 
end of the stroke. Because the condition of a generator blasting 
machine deteriorates with time, it is important that the machine 
be periodically checked with a riieostat designed for that purpose. 
The directions for testing with a rheostat are contained on the 
rheostat case or on the rheostat itself. Although the generator 
machine has been a dependable blasting tool, its limited capacity 
and variable output have caused it to be replaced, for most 
applications, by the condenser (capacitor) discharge machine. 

As the name implies, the capacitor discharge (CD) machine 
(fig. 24) employs dry cell batteries to charge a series of capacitors. 
The energy stored in the capacitor is then discharged into the 
blasting circuit. CD machines are available in a variety of 
designs and capacities, with some capable of firing over 1 ,000 
caps in a parallel series circuit. 

All CD machines operate in basically the same manner. 
One button or switch is activated to charge the capacitors and 
a second button or switch is activated to fire the blast. An 
indicator light or dial indicates when the capacitor is charged to 
its rated capacity. Ideally, the overall condition of a CD blasting 
machine should be checked with an oscilloscope. However, 
the current output can be checked by using a specially designed 
setup combining a rheostat and a resistor (2) or by using a 



26 




Figure 24.— Capacitor discharge blasting machine. (Courtesy du Pont co.) 



27 



capacitor discharge checking machine (7) . The powder supplier 
should be consulted as to the availability of machines for 
checking capacitor discharge machines. 

A sequential blasting machine (fig. 25) is a unit containing 
1 capacitor discharge machines that will fire up to 1 separate 
circuits with a preselected time interval between the individual 



circuits. When used in conjunction with millisecond delay electric 
blasting caps, the sequential machine provides a very large 
number of separate delay intervals (3). This can be useful in 
improving fragmentation and in controlling ground vibrations 
and airblast. Because blast pattern design and hookup can be 
quite complex, the sequential blasting machine should be 




Figure 25. — Sequential biasting machine. 



used only by well-trained persons or under the guidance of a 
consultant or a powder company representative. A poorly 
planned sequential timing pattem will result in poor fragmentation 
and excessive overbreak, flyrock, ground vibrations, and noise. 

The third alternative for energizing electric blasting circuits 
is the powerline. Powerline blasting is often done with parallel 
circuits where the capacity of available blasting machines is 
inadequate. When firing off a powerline, the line should be 
dedicated to blasting alone, should contain at least a 15-ft 
lightning gap, and should be visually checked for damage and 
for resistance on a regular basis. Powerline shooting should 
not be done unless precautions are taken to prevent arcing. 
Arcing can result in erratic timing, a hangfire, or a misfire. 

Arcing in a cap results from excessive heat buildup, which is 
caused by too much current applied for too long a period of 
time. A current of 10 amp or more continuously applied for a 
second or more can cause arcing. To guard against arcing the 
blaster may either use a blasting switch in conjunction with the 
powerline or add a No. 1 period millisecond delay cap, placed 
in a quarter stick of explosive, to the circuit and tape the 
explosive to one of the connecting wires leading to the cap 
circuit. An even better solution, if possible, is to use a high- 
output capacitor discharge machine to fire the shot, using a 
parallel series circuit if necessary. 



CIRCUIT TESTING 

It is important to check the resistance of the blasting circuit 
to make sure that there are no broken wires or short circuits 
and that the resistance of the circuit is compatible with the 
capacity of the power source. There are two types of blasting 
circuit testers; a blasting galvanometer (actually an ohmmeter) 
shown in figure 26 and a blasting multimeter, shown in figure 
27. The blasting galvanometer is used only to check the circuit 
resistance, whereas a blasting multimeter can be used to 
check resistance, ac and dc voltage, stray currents, and cur- 
rent leakage (2). Only a meter specifically designed for blast- 
ing should be used to check blasting circuits. The output of 
such meters is limited to 0.05 amp, which will not detonate an 
electric blasting cap, by the use of a silver chloride battery 
and/or internal current-limiting circuitry. 

Other equipment such as a "throw-away" go-no go device 
for testing circuits and a continuous ground current monitor is 
available. The explosive supplier should be consulted to deter- 
mine what specific electrical blasting accessory equipment is 
available and what equipment is needed for a given job. 

It is generally recommended that each component of the 
circuit be checked as hookup progresses. After each compo- 
nent is tested, it should be shunted. Each cap should be 
checked after the hole has been loaded and before stemming. 
In this way, a new primer can be inserted if a broken leg wire is 
detected. A total deflection of the circuit tester needle (no 
resistance) indicates a short circuit. Zero deflection of the 
needle (infinite resistance) indicates a broken wire. Either 
condition will prevent a blasting cap, and possibly the whole 
circuit, from firing. 

Before testing the blasting circuit, its resistance should be 
calculated. After the caps have been connected into a circuit 
the resistance of the circuit is checked and compared with the 
calculated value. A zero deflection at this time indicates a 
broken wire or a missed connection and an excessive deflec- 
tion indicates a short circuit between two wires. 

After the circuit resistance has been checked and compared, 
the connecting wire is then added and the circuit is checked 
again. If a parallel series circuit is used, the change in resis- 



tance should be checked as each series is added to the bus 
wire. In a straight parallel circuit, a break in the bus wire can 
sometimes be detected. However, a broken or a shorted cap 
wire cannot be detected in a straight parallel circuit because it 
will not affect the resistance significantly. 

A final check of the circuit is made at the shotfirer's location 
after the firing line has been connected. If a problem is found in 
a completed circuit, the circuit should be broken up into sepa- 
rate parts and checked to isolate the problem. The firing line 
should be checked for a break or a short after each blast, or at 
the end of each shift, as a minimum. 

To check for a break in the firing line, the two wires at one 
end of the line are shunted and the other end is checked with a 
blasting meter. A large deflection indicates that the firing line is 
not broken; a zero deflection indicates a broken wire. To test 
for a short, the wires at one end of the lead line are separated 
and the other end is checked with the meter. A zero deflection 
should result. If there is a deflection, the lead line has a short 
circuit. Embarassing, hazardous, and costly misfires can be 
avoided through proper use of the blasting galvanometer or 
blasting multimeter. 

Certain conditions such as damaged insulation, damp ground, 
a conductive ore body, water in a borehole, bare wires touch- 
ing the ground, or bulk slurry in the borehole may cause 
current to leak from a charged circuit. Although this is not a 
common occurrence, you may want to check for it if you are 
experiencing unexplained misfires. To properly check for cur- 
rent leakage you should check with a consultant or an electric 
blasting handbook (2). Measures for combating current leak- 
age include using fewer caps per circuit, using heavier gage 
lead lines and connecting wires, keeping bare wire connec- 
tions from touching the ground, or using a nonelectric initiation 
system. 




Figure 26.— Blasting galvanometer. (Courtesy du Pont c«.) 



29 






u 


H 


|H 






TT 



Figure 27. — Blasting multimeter. (Courtesy du Pont co.) 



30 



EXTRANEOUS ELECTRICITY 

The principal hazard associated with electric blasting sys- 
tems is lightning. Extraneous electricity in the form of stray 
currents, static electricity, and radiofrequency energy, and 
from high-voltage powerlines can also be a hazard. Electric 
blasting caps should not be used in the presence of stray 
currents of 0.05 amp or more. Stray currents usually come 
from heavy equipment or power systems in the area, and are 
often carried by metal conductors or high-voltage powerlines. 
Atlas (2) outlines techniques for checking for stray currents. 
Instruments have recently been developed which continu- 
ously monitor ground currents and sound an alarm when an 
excess current is detected. The supplier should be consulted 
as to the availability of these units. 

Static electhcity may be generated by pneumatic loading, 
particles carried by high winds, particularly in a dry atmosphere, 
and by rubbing of a person's clothes. Most electric blasting 
caps are static resistant. When pneumatically loading blasting 
agents with pressure pots or venturi loaders, a semiconductive 
loading hose must be used, a plastic borehole liner should not 
be used, and the loading vessel should be grounded. 

Electrical storms are a hazard regardless of the type of 
initiation system being used. Even underground mines are 
susceptible to lightning hazards. Upon the approach of an 
electrical storm, loading operations must cease and all person- 
nel must retreat to a safe location. The powder manufacturer 
should be consulted on the availability of commercial storm 
warning devices. Some operators use static on an AM radio as 
a crude detector of approaching storms. Weather reports are 
also helpful. 

Broadcasting stations, mobile radio transmitters, and radar 
installations present the hazard of radiofrequency energy. The 
IME (11) has prepared charts giving transmission specifica- 
tions and potentially hazardous distances. 



High-voltage powerlines present the hazards of capacitive 
and inductive coupling, stray current, and conduction of lightning. 
Atlas (2) details precautions to be taken when blasting near 
high-voltage powerlines. A specific hazard with powerlines is 
the danger of throwing part of the blasting wire onto the powerline. 
This shorts the powerline to the ground and has been responsi- 
ble for several deaths. Care should be exercised in laying out 
the circuit so that the wires cannot be thrown on a powerline. 
Other alternatives are to weigh down the wires so they cannot 
be thrown or attach a charge that cuts the blasting wire. 



ADDITIONAL 
CONSIDERATIONS 

Electric blasting is a safe, dependable system when used 
properly under the proper conditions. Advantages of the sys- 
tem are its reasonably accurate delays, ease of circuit testing, 
control of blast initiation time, and lack of airblast or disruptive 
effect on the explosive charge. In addition to extraneous 
electricity, one should guard against kinks in the cap leg wires, 
which can cause broken wires, especially in deep holes. Differ- 
ent brands of caps may vary in electric properties, so only one 
brand per blast should be used. It is recommended that the 
blaster carry the key or handle to the power source on his or 
her person so the shot cannot be inadvertently fired while he or 
she is checking out the shot. 

A device called an exploding bridge wire is available for use 
where a single cap is used to initiate a nonelecthc circuit. This 
device has the safety advantages of a lack of primary explo- 
sive in the cap and a high voltage required for firing. A special 
firing box is required for the system. The high power required 
and high cost of the exploding bridge wire device make it 
unsuitable for use in multicap circuits. 



DETONATING CORD INITIATION 



Detonating cord initiation has been used for many years as 
an alternative to electric blasting where the operator prefers 
not to have an electric initiator in the blasthole. Detonating 
cord (fig. 28) consists of a core of high explosive, usually 
PETN, contained in a waterproof plastic sheath enclosed in a 
reinforcing covering of various combinations of textile, plastic, 
and waterproofing. Detonating cord is available with PETN 
core loadings ranging from 1 to 400 gr/ft. 

All cords can be detonated with a blasting cap and have a 
detonation velocity of approximately 21 ,000 fps. Detonating 
cord is adaptable to most surface blasting situations. When 
used in a wet environment the ends of the cord should be 
protected from water. PETN will slowly absorb water and as a 
result will become insensitive to initiation by a blasting cap. 
Even when wet, however, detonating cord will propagate if 
initiated on a dry end. Understanding the function of a detonat- 
ing cord initiation system requires a knowledge of the products 
available. The Ensign Bickford Co. has published a manual (8) 
that describes detonating cord products in detail. Technical 
data sheets are available from Austin Powder Co. and Apache 
Powder Co. 



DETONATING 
CORD PRODUCTS 

The most common strengths of detonating cord are from 25 
to 60 gr/ft. These strengths are used for trunklines, which 
connect the individual blastholes into pattern, and fordownlines, 
which transmit the energy from the trunkline to the primer 
cartridge. The lower strength cords are cheaper, but some 
have less tensile strength and may be somewhat less depend- 
able under harsh field conditions. Some cast primers are not 
dependably initiated by 25-gr cord or lighter cord. However, 
under normal conditions, the lighter core loads offer economy 
and their greater flexibility makes field procedures such as 
primer preparation and knot tying easier. 

Detonating cord strengths of 100 to 200 gr/ft are occasion- 
ally used where continuous column initiation of a blasting 
agent is desired. Cords with 200 to 400 gr of PETN per foot are 
occasionally used as a substitute for explosive cartridges in 
very sensitive or small, controlled blasting jobs. Controlled 
blasting is described in the "Blast Design" chapter. 



31 



-. - ~'^'.^7I?^^^^S^~Z3^ 



2000 FT A- CORD 
CORDEAU DETONANT FUSE 




AUSTIN POWDER COMPANY 

CLEVELAND. OHIO US^i.*'*^ 




Figure 28.— Detonating cord. (Courtesy Austin Powder Co.) 



Detonating cord strengths lower than 25 gr/ft are sometimes 
used. Fifteen- to twenty-grain products may be used for small- 
diameter holes, for secondary blasting, and in the Nonel sys- 
tem described later. A 7.5-gr cord is also used in the Nonel 
system. A 4-gr/ft product is used as part of an assembly called 
a Primaline Primadet. A Primaline Primadet consists of a 
length of 4-gr cord crimped to a standard instantaneous or 
delay blasting cap. The cap is inserted into the primer and the 
4-gr cord serves as a downline. Various cord lengths are 
available to suit specific borehole depths. These Primadets 
are primarily used in underground mines, such as salt, where 
Nonel tubes would be a product contaminant. Du Pont's new 
Detaline System utilizes a 2.4-gr cord. 

Millisecond delay surface connectors are used for delaying 
detonating cord blasts. To place a delay between two holes, 
the trunkline between the holes is cut and the ends are joined 
with a delay connector. One type of delay connector is a 
plastic assembly containing a delay element (fig. 29). At each 
end of the element is an opening into which a loop of the 
severed trunkline can be inserted. A tapered pin is used to lock 
the trunkline cord into place. A Nonel delay connector has also 
been developed for detonating cord blasting (fig. 30). This 



connector consists of two plastic blocks, each containing a 
delay initiator, connected by a short length of Nonel tubing. 
Each end of the severed trunkline is wrapped around the notch 
in one of the plastic blocks. Both types of delay connector are 
bidirectional. 



FIELD APPLICATION 

After the primer has been lowered to its proper location in 
the blasthole, the detonating cord is cut from the spool. About 
2 or 3 ft of cord should extend from the hole to allow for charge 
settlement and tying into the trunkline. When the entire shot 
has been loaded and stemmed, the trunkline is laid out along 
the path of desired initiation progression. Trunkline-to-trunkline 
connections are usually made with a square knot. A tight knot, 
usually a clove hitch, a half hitch, or a double-wrap half hitch, is 
used to connect the downline to the trunkline (fig. 31). Any 
excess cord from the downline should be cut off and disposed. 
If Primadets or other in-hole delay assemblies are used, a 
plastic connector often serves as the connection to the trunkline. 
The cord lines should be slack, but not excessively so. If too 



32 



f^l 




Figure 29. — Clip-on surface detonating cord delay connector. (Courtesy Hercules inc.) 




Figure 30.— Nonel surface detonating cord delay connector. (Courtesy Ensign Bickford co.) 



33 



Downline to Trunkline Connections 



d^ 





Figure 31 .—Recommended knots for detonating cord. 



much slack is present, the cord may cross itself and possibly 
cause a cutoff (fig. 32). Also, if the lines are too tight and form 
an acute angle, the downline may be cut off without detonating. 
Downlines of detonating cord can adversely affect the col- 
umn charge of explosive in the blasthoie. With cap-sensitive 
explosives, continuous, axial initiation will occur with any cord 
containing 1 8 or more grains of PETN per foot of cord. Lower 
strength cords may also cause axial initiation. Four-grain cord 
will not initiate most cap-sensitive explosives. With blasting 
agents, the effect of detonating cord is less predictable. The 
blasting agent may be desensitized or it may be marginally 
initiated. Hagan (10) has studied this problem. The effect 
depends on the cord strength, blasting agent sensitivity, blasthoie 
diameter, and position of the cord within the blasthoie. As a 
general rule, 50-gr cords are compatible with blasthoie diame- 
ters of 8 in or more. In charge diameters of 5 to 8 in, 25-gr or 




TIGHT LINE 




1 1 1 I 1 1 1 1 1 1 1 1 1 rj{7 / 1 1 1 1 1 1 1 1 I 

Direction of propagation 

Figure 32.— Potential cutoffs from slacit and tiglit det- 
enating cbrdlines. 



lighter downlines should be used. In diameters below 5 in, 
low-energy (4- to 10-gr) downlines or alternative, nondisrup- 
tive initiation systems are recommended. The manufacturer 
should be consulted for recommendations on the use of deto- 
nating cord with various explosive products. A low-energy 
initiation system called Detacord, developed by du Pont, is 
described later in this chapter. 



DELAY SYSTEMS 

Surface delay connectors offer an unlimited number of delays. 
For instance, a row of 100 holes could be delayed individually 
by placing a delay between each hole and initiating the row 
from one end. Typical delay intervals for surface connectors 
are 5, 9, 1 7, 25, 35, 45, and 65 ms. Since these connectors are 
normally used for surface blasting, half-second delay periods 
are not available. 

Cutoffs may be a problem with surface delay connectors. 
When the powder column in one hole detonates, the connec- 
tions between holes to be fired later may be broken by crater- 
ing or other movement of the rock mass. This may cause a 
subsequent hole to misfire. To correct this situation, MSHA 
requires that the pattern of trunklines and delay connectors be 
designed so that each blasthoie can be reached by two paths 
from the point of initiation of the blast round. The patterns can 
become somewhat complex and should be laid out and care- 
fully checked on paper before attempting to lay them out in the 
field. Where possible the pattern should be designed so that 
the delay sequence in which the holes fire is the same no 
matter which path is taken from the point of blast initiation. The 
"Blast Design" chapter gives suggestions for selecting the 
actual delay inten/als between blastholes. 

Figure 33 shows a typical blast laid out with delay connectors. 
Note that each hole can be reached by two paths from the 
point of initiation. A time of 1 ms is required for 21 ft of 
detonating cord to detonate. This time is not sufficient to 
significantly alter the delay interval between holes. 

When detonating cord downlines are used, detonation of 
the cord in the blasthoie proceeds from the top down. This 
presents two disadvantages. First, the detonation of the cord 
may have an undesirable effect on the column charge as it 
proceeds downward and the stemming may be loosened. 
Second, if the hole is cut off by burden movement caused by 
detonation of an earlier hole (fig. 34) the powder in the lower 
portion of the hole will not detonate. The use of a Primaline 



I 




Point of 
Initiation 



KEY 
X Dtloy connector 
,6 Delay period of blosthole 

Figure 33.— Typical blast pattern with surface 
delay connectors. 



34 



Detonating 
cord 




Figure 34. — Misfire caused by cutoff from burden 
movement. 



Primadet delay unit in the hole will correct both of these 
problems. 

The Primaline Primadet is a delay cap attached to a length 
of 4-gr/ft detonating cord. It is available in both millisecond and 
long delay periods. The Primaline Primadet is connected to 
the trunkline with a plastic connector or a double-wrap half 
hitch. If the delay pattern of the blast is such that the number of 
available Primadet delay periods is adequate, an undelayed 
trunkline may be used. The delay period of the cap would then 
be the delay period of the hole. As an example, to attain the 
delay pattern in figure 33, cap delay periods one through nine 
would be placed in the appropriate holes and trunklines would 
contain no delays. In this situation, the delay in every cap 
would be actuated before the first hole detonates. This would 
reduce the chance of a cutoff. The 4-gr Primaline Primadet is 
steadily being replaced by other nonelectric systems, described 
later in this chapter. 

Another alternative to obtain the delay pattern in figure 33, 
and avoid the cutoff problem, would be to use the array of 
surface delays shown in the figure and an in-hole delay of an 
identical period in each blasthole. For instance, if a 75-ms 
delay is used in each hole, and the trunkline delays are each 9 
ms, the delays in all of the holes except the two rear corner 
holes will be actuated before the first hole in the pattern fires, 
thus alleviating the cutoff problem. More complex patterns 
involving both surface and in-hole delays can be designed 
where desirable. An alternative method of obtaining in-hole 
delays with detonating cord is to use delay cast primers (fig. 
12). These are cast primers with built-in nonelectric millisec- 



ond delays. They can be strung on detonating cord downlines 
of 25 gr or more and are particularly useful in obtaining multi- 
ple delayed deck charges with a single downline. It bears 
repeating that delay patterns involving both surface and in-hole 
delays can be somewhat complex and should be carefully laid 
out on paper before attempting to install them in the field. 



GENERAL CONSIDERATIONS 

Two of the primary advantages of detonating cord initiation 
systems are their ruggedness and their insensitivity. They 
function well under severe conditions such as in hard, abra- 
sive rock, in wet holes, and in deep, large-diameter holes. 
They are not susceptible to electrical hazards, although light- 
ning is always a hazard while loading any blast. Detonating 
cord is quite safe from accidental initiation until the initiating 
cap or delay connectors are attached. Available delay sys- 
tems are extremely flexible and reasonably accurate. 

There are several disadvantages that may be significant in 
certain situations. Systems employing only surface connec- 
tors for delays present the potential for cutoffs. Surface con- 
nectors also present the hazard of accidental initiation by 
impact. Detonating cord trunklines create a considerable amount 
of irritating, high-frequency airblast (noise). In populated areas 
the cord should be covered with 1 5 to 20 in of fine material or 
alternative, noiseless systems should be used. Detonating 
cord downlines present the problem of charge or stemming 
disruption. As discussed previously, this depends on the bore- 
hole diameter, the type of explosive, and core load of explo- 
sive in the cord. The means of checking the system is visual 
examination. 

Vehicles should never pass over a loaded hole because the 
detonating cord lines may be damaged, resulting in a misfire 
or premature ignition. A premature ignition could result from 
driving over a surface delay connector. 



DETALINE SYSTEM 

Du Pont's Detaline System is a recently developed initiation 
system that is based on low-energy detonating cord. It func- 
tions similarly to conventional detonating cord systems except 
that the trunkline is low in noise, downlines will not disrupt the 
column of explosive, it will not initiate blasthole products, 
except dynamites, and all connections are made with connectors, 
rather than knots. The four components of the system are 
Detaline Cord, Detaline Starters, Detaline MS Surface Delays, 
and Detaline MS In-Hole Delays. 

The Detaline Cord (Detacord) is a 2.4-gr/ft detonating cord 
whose appearance is similar to standard detonating cord. The 
cord is cut to lengths required for the blast pattern. This low- 
energy cord, while low in noise, has sufficient energy to disinte- 
grate the cord upon detonation, which is advantageous where 
contamination of the blasted product must be avoided. Detacord 
will not propagate through a knot, which is why connectors are 
required. To splice a line or to make a nondelayed connection, 
a Detaline Starter is required. The body of the starter is shaped 
much like a clip-on detonating cord millisecond delay connector, 
except that the starter is shaped like an arrow to show the 
direction of detonation. To make a splice, the starter is con- 
nected to the two ends of the Detacord using the attached 
sawtooth pin, making sure that the arrow points in the direction 
of detonation. To make a connection, the donor trunkline is 
hooked into the tail of the starter and the acceptor trunkline, or 
downline, is hooked into the pointed end of the connector. 



35 



The Detaline System has provisions for both surface and 
in-hole delays. The surface delays, which come in periods of 
9, 17 , 30, 42, 60, and 100 ms, are shaped like the starter but 
are colored according to the delay. The surface delays are 
also unidirectional, with the arrow showing the direction of 
detonation. The surface delays can be hooked into a trunkline 
in which case their function is similar to that of a standard 
millisecond delay connector. They can also be used as starters, 
connected between the trunkline and downline at the collar of 
the blasthole. In this situation the delay affects only the downline, 
and not the trunkline. 

A Detaline MS In-Hole Delay resembles a standard blasting 
cap except for a special top closure for insertion of the Detacord. 
It functions similarly to a surface delay. Nineteen delay periods, 
ranging from 25 to 1,000 ms, are available. The delay is 
connected to the downline and is inserted into the primer. 

Hookup of the Detaline System is similar to conventional 
detonating cord except that connectors are used rather than 
knots and right-angle connections are not necessary. When it 
Is time to hook up, the Detaline trunkline is reeled out over the 
length of each row. Each downline is connected to the arrow 
end of a starter or a surface delay. The tail of each starter or 
surface delay is then connected into the trunkline. The open 
sides of the pattern are then connected in a manner similar to 
conventional detonating cord systems using Detacord and 
appropriate starters and surface delays. It is essential that all 



Detacord-to-Detacord connections be made with starters or 
surface delays rather than knots. 

The Detaline System bears many similarities to conven- 
tional detonating cord systems. The system is checked out 
visually before firing. Combining surface and in-hole delays 
gives a practically unlimited number of delay combinations. It 
is convenient to build redundancy into the system. At firing 
time, the end of the trunkline tail extending from the shot is 
placed into the arrow end of a starter, and an electhc or fuse 
blasting cap is inserted into the tail end of the starter and 
Initiated. 

The detonation energy of the 2.4-gr Detacord is adequate to 
disintegrate the trunkline. However, the resulting trunkline 
noise is quite low; typically about 13 dB lower than 25-gr 
detonating cord in field trials. A downline of Detacord will 
detonate most dynamites but will not detonate most water 
gels. A major advantage of a Detacord downline is that it will 
not disrupt a column of blasting agent. Detacord can be used 
as a total system or in conjunction with some standard detonat- 
ing cord components. As with most newer systems, evolution- 
ary changes may occur in the coming years. It is important that 
the manufacturer be consulted for recommended procedures 
for using Detacord. The manufacturer will also be able to 
recommend which variation of the system best suits a particu- 
lar field situation. 



CAP-AND-FUSE INITIATION 



Cap and fuse is the oldest explosive initiation system; however. 
Its use has dwindled steadily. Its primary remaining use is in 
small underground mines, although a few large mines still use 
It. Surface applications are limited to secondary blasting and 
the initiation of detonating cord rounds with a single cap. 



COMPONENTS 

The detonator used in a cap-and-fuse system is a small 
capsule that is open at one end (fig. 35). The capsule contains 
a base charge and a heat-sensitive primer charge of explosive. 
The powder charge in the cap is initiated by a core of flamma- 
ble powder in the safety fuse. Safety fuse has an appearance 
somewhat similar to detonating cord except that the surface of 
safety fuse is smoother and more waxy and the core load is 
black. The core load of detonating cord is white. 

To assemble a cap and fuse, the fuse is carefully cut squarely 
and inserted into the cap until it abuts against the explosive 
charge in the cap. The fuse should never be twisted against 
the explosive charge in the cap. The cap is then crimped near 
the open end with an approved hand or bench crimper. The 




^Bose 
chorge charge 



Figure 35.— Blasting cap for use with safety fuse. 



crimp should be no more than three-eighths of an inch from the 
open end of the cap. 



FIELD APPLICATIONS 

Currently, all safety fuse burns at the nominal rate of 40 
sec/ft. Both dampness and high altitude will cause the fuse to 
burn more slowly. Fuse should be test burned periodically so 
that the blaster can keep a record of its actual burning rate. 
"Fast fuse" has been blamed for blasting accidents but the 
fact is that this rarely if ever occurs. However, pressure on the 
fuse may increase its burning rate. 

One of the most important considerations in the use of 
cap-and-fuse systems is the use of a positive, approved light- 
ing mechanism. Matches, cigarette lighters, carbide lamps, or 
other open flames are not approved for lighting fuse. MSHA 
regulations specify hotwire lighters, lead spitters, and Ignitacord 
as approved ignition systems. The safest, most controllable 
lighting method is Ignitacord. In South Africa, where safety 
fuse is most often sold as an assembly with an Ignitacord 
connector attached, the safety record with cap and fuse is 
much better than it is in the United States. 

The Ignitacord connector fits over the end of the fuse and is 
crimped in a manner similar to the cap. Figure 36 shows a 
typical cap, fuse, and Ignitacord assembly. The cap is attached 
to the fuse with a bench or hand crimper, and never with the 
teeth or pliers. When crimping the cap, care should be taken 
not to crimp the zone containing the powder. The Ignitacord 
connector is crimped to the other end of the fuse with a hand 
crimper. The Ignitacord is inserted into the notch near the end 
of the connector and the notch is closed using the thumb. 

To guard against water deterioration, it is a good idea to cut 
off a short length of fuse immediately before making cap-and- 



36 



COMPONENTS 



Ignitocord 




-Ignitacord 

Figure 36.— Cap, fuse, and Ignitacord assembly. 



fuse assemblies. In deciding the length of fuse to cut for each 
primer, the lighting procedure must be considered. Ignitacord 
is strongly recommended because of its safety record. 

When Ignitacord is used, each fuse must have a burning 
time of at least 2 min. To make sure of this time, the fuse must 
be calibrated periodically by test burning. The Ignitacord is 
attached to the Ignitacord connectors in the desired order of 
firing. If all the fuses are cut accurately to the same length, the 
desired order of firing will be achieved. 

With Ignitacord, only one lighting is required before the 
shotfirer returns to a safe location. Hotwire lighters and lead 
spitters require that each fuse be lit individually. The primary 
hazard of using safety fuse is the tendency of blasters to linger 
too long at the face, making sure that all the fuses are lit. To 
guard against this, MSHA regulations specify minimum burn- 
ing times for fuses, depending on how many fuses one person 
lights. Keep in mind that two persons are required to be at the 
face while lighting fuse rounds. 

If a person lights only one fuse, the minimum burning time is 
2 min; for 2 to 5 fuses the minimum is 2-2/3 min; for 6 to 10 
fuses the minimum is 3-1/3 min; and for 11 to 15 fuses the 



minimum is 5 min. One person may not light more than 15 
fuses in a round. Although individual fuse lengths may be 
varied for delay purposes it is more dependable to cut all the 
fuses to the same length and use the sequence of lighting to 
determine the firing sequence. 

To avoid misfires due to cutoff fuses, MSHA requires that 
the fuse in the last hole to fire is burning within the hole before 
the first hole fires. Kinks and sharp bends in the fuse should be 
avoided because they may cut off the powder train and cause 
a misfire. Many people who use cap and fuse do so because 
they feel that it is simpler to use than other initiation systems. 
However, proper use of cap and fuse requires as much or 
more skill and care as the other systems. 



DELAYS 

Cap and fuse is the only initiation system that offers neither 
flexibility nor accuracy in delays. Because of variations in 
lengths of fuse, burning rates, and time of lighting the individ- 
ual holes will fire at erratic intervals at best, and out of sequence 
at worst. It is impossible to take advantage of the fragmenta- 
tion benefits of millisecond delays when using the cap-and- 
fuse system. 



GENERAL CONSIDERATIONS 

There is no situation in which cap and fuse can be recom- 
mended as the best system to use. The system has two 
overpowering flaws — inaccurate timing and a poor safety record. 
The former results in generally poor fragmentation, a higher 
incidence of cutoffs, and less efficient pull of the round. All of 
these factors nullify the small cost advantage derived from the 
slightly lower cost of the system components. The poor safety 
record attained by cap and fuse is an even more serious 
drawback. It is the only system that requires the blaster to 
activate the blast from a hazardous location and then retreat to 
safety. The use of Ignitacord rather than individual fuse light- 
ing alleviates this problem. A Bureau study (14) determined 
that the accident rate with cap and fuse is 17 times that of 
electric blasting, based on the number of units used. Too 
often, the person lighting the fuse is still at the face when the 
round detonates. The time lag between lighting the fuse and 
the detonation of the round makes security more difficult than 
with other systems. 

Cap and fuse does have the advantages of lack of airblast, 
no charge disruption, somewhat lower component costs, and 
protection from electrical hazards. If an operator decides to 
use the cap-and-fuse system, incorporation of Ignitacord for 
lighting multiple holes is strongly recommended because of its 
safety record. 



OTHER NONELECTRIC INITIATION SYSTEMS 



Beginning about in 1 970, efforts were devoted toward develop- 
ing new initiation systems that combined the advantages of 
electric and detonating cord systems. Basically, these sys- 
tems consist of a cap similar to an electric blasting cap, with 
one or two small tubes extending from the cap in a manner 
similar to leg wires. Inside these tubes is an explosive material 
that propagates a mild detonation which activates the cap. 



Delay periods similar to those of electric blasting caps are 
available except that there are no coal mine delays, since 
these devices are not approved for use in underground coal 
mines. These initiation systems are not susceptible to extrane- 
ous electricity, create little or no airblast, do not disrupt the 
charge in the blasthole, and have delay accuracies similar to 
those of electric or detonating cord systems (5). 



37 



At the time this manual was written, two relatively new 
nonelectric initiation systems — Hercudet and Nonel — were 
on the market. Other nonelectric systems are either under 
development or in the conception stage. Both Hercudet and 
Nonel were introduced to the U.S. market in the mid-1 970's. 
Because of their relative recency, minor changes are still 
being made in these systems. The following discussions are 
intended to give only general information on the systems. 
Persons planning to use the systems should contact the 
manufacturers, Hercules Inc. and Ensign Bickford Co., 
respectively, for specific recommendations on their use. A 
third system, du Font's Detaline System, is discussed in the 
"Detonating Cord Initiation" section of this chapter. 



HERCUDET 

The hookup of the Hercudet (also called gas detonation) 
blasting system resembles a plumbing system. The cap is 
higher strength than most electric blasting caps. Both millisec- 
ond and long delays are available. Instead of leg wires, two 
hollow tubes protrude from the cap. The cap may be used in a 
primer in the hole or at the collar of the hole for initiating 
detonating cord downlines. In addition to the Hercudet cap, 
system accessories include duplex trunkline tubing, single 
trunkline tubing; various types of tees, connectors, ells, and 
manifolds for hooking up the system; circuit testers; a gas 
supply unit containing nitrogen, oxygen, and fuel cylinders; 
and a blasting machine. The system functions by means of the 
bw-energy detonation of an explosive gas mixture introduced 
into the hollow tubes. This low-energy detonation does not 
burst or othenwise affect the tubing. 



For surface blasting, a cap with 4-in leads is used (fig. 37). 
For surface initiation of detonating cord downlines this cap is 
connected directly to the trunkline tubing by means of the 
reducing connector that is factory-attached to the cap. The 
reducing connector is needed because the trunkline tubing is 
larger than the capline tubing. A special plastic connector is 
used to attach the cap to the detonating cord downline. 

When in-hole initiation is desired, the 4-in cap leads are 
extended by connecting them to an appropriate length of 
larger diameter duplex trunkline tubing (fig. 38). This trunkline 
tubing is cut squarely, leaving 2 to 3 ft of tubing extending from 
the borehole collar, and a plastic double ell fitting is inserted. 
Trunkline tubing is later connected hole to hole. Figure 39 
shows typical Hercudet connections for surface blasting with 
in-hole delays. 

Not all cast primers have tunnels large enough to accept the 
Hercudet duplex tubing. This should be checked before pur- 
chasing cast primers. When using cartridge primers with 
Hercudet, the tubing is taped to the primer, not half-hitched to 
it. 

For undergrouno oiasting, millisecond and long period delay 
caps are available with 1 6- to 24-ft lengths of tubing. The tubes 
are cut to the appropriate length by the blaster. The tubes are 
then connected in series or series-in-parallel, similar to elec- 
tric cap circuits, using capline connectors and manifolds instead 
of the wire splices used in electric blasting. In all Hercudet 
blasting circuits, the tubing at the end of each series is vented 
to the atmosphere. The tubing network should be kept free of 
kinks. 

When the circuit has been hooked up, a length of trunkline 
tubing is strung out to the firing position, similar to the firing line 
in an electric system. At this time nitrogen from the gas supply 




Figure 37.— Hercudet blasting cap with 4-in tubes. (Courtesy Hercules inc.) 



38 




Figure 38.— Extending Hercudet leads with duplex tuoing. (Courtesy Hercules inc.) 



ctb^Doubi. .11 cttv^B 




Blasthole-^ 

Figure 39.— Hercudet connections for surface blasting. 



unit is turned on and the pressure test module is used to check 
the integrity of the tube circuit (fig. 40). The tester uses flow 
and/or pressure checl<s to locate blockages or leaks in the 
circuit. As with a galvanometer in electric blasting, each series 
should be checked individually, followed by a check of the 
entire system. The Hercudet tester is a smaller unit than the 
pressure test module and uses a hand air pump to test single 
boreholes or small hookups (fig. 41). If a plug or a leak is 
detected when checking the completed circuit, the circuit is 
broken into segments and checked with the Hercudet tester or 
pressure test module. 

Once the system has been checked and the blast is ready to 
fire, the blasting machine, connected to the bottle box (gas 
supply unit), is used to meter a fuel and oxidizer mixture into 
the firing circuit (fig. 42). Until this detonable gas mixture is put 
into the tubes, the connections between the caps are totally 
inert. The explosive gas must be fed into the system for an 
adequate period of time to assure that the system is entirely 
filled. Gas feeding continues until the blaster is ready to fire the 
shot. The time required to charge the circuit with gas depends 
on the size of the circuit. 



39 




Figure 40.— HerCUdet pressure test module. (Courtesy Hercules inc.) 



When the system has been charged, the blasting machine 
control lever is moved to "arm" and the "fire" button is pushed, 
causing a spark to ignite the gas mixture. A low-energy gas 
detonation travels through the tubing circuit and through the 
air space inside the top of each individual cap at a speed of 
8,000 fps and ignites the delay element in the cap. 

The relatively slow (8,000 fps) detonation rate of the gas 
introduces an additional delay element into the system. For 
instance, assuming a gas detonation rate of 8 ft/ms, with caps 
at a depth of 30 ft in blastholes spaced 1 2 ft apart (a total travel 
path of 72 ft from cap to cap), a 9-ms delay between caps will 
be introduced by the tubing. It is essential that these tube 
delays be taken into account when calculating the actual firing 
times of the individual caps. Although the calculations are not 
complex, it is important that they are done carefully, before 
hooking up the blast, to avoid possible errors in the last minute 
rush to get the shot off. The delay time of the tubing can be 
used to advantage by coiling tubing in the trunkline at any 
location where an additional surface delay is desired. 

The Hercudet system has the advantages of no airblast, no 
charge disruption, no electrical hazards, versatile delay capability, 
and system checkout capability. The inert nature of the system 
until the gas is introduced is a safety benefit. Specific crew 
training by a representative of the manufacturer is necessary 
because the system is somewhat different in principle than the 
older systems such as detonating cord and electric blasting. 
Care must be taken not to get foreign material such as dirt or 
water inside the tubing or connector while hooking up the shot, 
and to avoid knots or kinks in the tubing. 



NONEL 

The hookup of the Nonel (also called the shock tube) sys- 
tem is similar in some respects to the detonating cord system. 
The cap used in the system is higher strength than most 
electric blasting caps. Instead of leg wires, a single hollow tube 
protrudes from the cap (fig. 43). The Nonel tube has a thin 
coating of reactive material on its inside surface, which deto- 
nates at a speed of 6,000 fps. This is a very mild dust explosion 
that has insufficient energy to damage the tube. Several varia- 
tions of the Nonel system can be used, depending on the 
blasting situation. In addition to the Nonel tube-cap assembly, 
system accessories include noiseless trunklines with built-in 
delays, noiseless lead-in lines, and millisecond delay connec- 
tors for detonating cord trunklines. 

One Nonel system for surface blasting uses a Nonel Primadet 
in each blasthole with 25- to 60-gr/ft detonating cord as a 
trunkline. The Nonel cap used in this system is factory crimped 
to a 24-in length of shock tube with a loop in the end (fig. 44). 
The caps are available in a variety of millisecond delay periods. 
A 7.5-gr detonating cord downline is attached to the loop with a 
double-wrapped square knot. The 7.5-gr detonating cord extends 
out of the borehole. This downline will not disrupt a column 
charge of blasting agent but it may initiate dynamite and other 
cap-sensitive products. As a precaution, 7.5-gr to 7.5-gr con- 
nections should never be made, because propagation from 
one cord to the other is not dependable. Since the force of the 
shock tube detonation is not strong enough to disrupt the tube, 
it will not initiate high explosives. A 25- to 60-gr trunkline is 




Figure 41. — HerCUdet tester for small hookups. (Courtesy Hercules inc.) 



used in this system with a double clove hitch used for downline- 
to-trunkline connections. The delay systems used with this 
method of initiation are the same as those discussed in the 
"Detonating Cord Initiation" section. They include in-hole cap 
delays and surface delay connectors. 

In some cases this system creates an excessive amount of 
airblast and noise. To prevent this, the detonating cord trunkline 
can be replaced by an electric blasting cap circuit with a cap 
connected to each downline, or a noiseless Nonel trunkline 
can be used. 

The noiseless Nonel trunkline is employed as follows. First, 
each hole is primed and loaded. The downline should be an 
1 8-gr or larger detonating cord. A 7.5-gr downline can be used 
if a 25-gr pigtail is used at the top end, tied into the connector 
block. The noiseless trunkline delay unit consists of a length of 
shock tube, 20 to 60 ft in length, with a quick connecting sleeve 
on one end and a plastic block containing a millisecond delay 
blasting cap (delay assembly) on the other end, and a tag 
denoting the delay period (fig. 45). The delay may be from 5 to 
200 ms. 

The sleeve is attached to the initial hole to be fired and the 
shock tube is extended to the next hole in sequence. The 
downline from this next hole is connected to the plastic block 
containing the delay cap, using about€ifvof cord at the end of 
the downline. Another delay unit is selected and the sleeve is 
attached to the downline below the plastic block. The shock 
tube is extended to the next hole, where the delay assembly is 



connected to the downline. The process is repeated until all 
the holes are connected. Figure 46 shows a portion of a shot 
hooked up in this way. 

The downlines and the plastic blocks containing the delay 
cap should be covered to reduce noise and flying shrapnel. 
When the blaster is ready to fire the shot, an initiating device is 
attached to the downline of the first hole. This device may be 
an electric blasting cap, a cap and fuse, or a Nonel noiseless 
lead-in (fig. 47). A noiseless lead-in is a length of shock tube, 
up to 1 ,000 ft long, crimped to an instantaneous blasting cap. 
The shock tube is initiated by using an electric blasting cap, 
cap and fuse, or other initiating device recommended by the 
manufacturer. 

For underground blasting, millisecond and long period delay 
caps are available with 10- to 20-ft lengths of shock tube 
attached. Common practice is to use a trunkline of 1 8- or 25-gr 
detonating cord. The Nonel tube from each blasthole is attached 
to the trunkline with a J-connector. A simpler method is to use 
the bunching system, where up to 30 tubes are tied together 
parallel, in a bunch, and detonating cord is clove-hitched 
around the bunch. The manufacturer should be consulted to 
demonstrate the bunching technique and to determine the 
number of wraps of detonating cord required for a given size 
bunch. 

When pneumatic loading is used, a plastic cap holder can 
be utilized to center the cap in the hole and to reduce move- 
ment of the cap. It is important that the Nonel tube is in a 



41 




Figure 42.— Hercules bottle box and blasting machine. (Courtesy Hercules inc.) 




Figure 43. — Nonel blasting cap. (Courtesy Ensign BIckford Co.) 



42 




Figure 44. — Nonel Primadet cap for surface blasting. (Courtesy Ensign BicMord co.) 




DELAY ASSEIteLY 




Figure 45.— Nonel noiseless trunkline delay unit. 

(Courtesy Ensign BIckford Co.) 



Figure 46.— Noiseless trunkline using Nonel delay 
assemblies. 



straight line, fairly taut, and that crossovers or contact with the 
trunkline are avoided. This is true in all Nonel blasting but 
particularly in heading rounds, where the blast face is more 
crowded. Just before blasting, an electric cap or cap and fuse 
is connected to the trunkline. 

The Nonel system has the advantages of no airblast (when 
a noiseless trunkline is used), no charge disruption (when 
Nonel tube or a 7.5-gr cord in conjunction with a Nonel Primadet 
is used as a downline), no electrical hazards, and a versatile 
delay capability. Keep in mind that electrical storms are a 
hazard with any initiation system. System checkout is done 
through visual inspection. Nonel shock tube assemblies should 
never be cut or trimmed, as that may cause the system to 
malfunction. The shock tube will initiate nothing but the cap 
crimped onto it. Because of the variations available and new 
concepts involved, specific crew training by a manufacturer's 
representative is highly recommended before using the Nonel 
system. 




-NONEIL 

Primadet* 

NOISIUSS UAD-IM UME 



PiRlOO O 

/ooo 



Fcn 



»OOl N0.2£Sii 



s 



xiz^ 



MiCEt 

•usrmc 




/9^1 



'IKMI CNIUNKN 



i^nsign Bickfford 

Wmskury. Conn. 06070 



'^ 



3o / 






Figure 47. — Nonel noiseless lead-in line. (Courtesy Ensign BIcMord Co.) 



PRIMING 



Essentially, the term primer is used to describe a unit of 
cap-sensitive explosive that contains a detonator, while the 
term t)ooster describes a unit of explosive that may or may not 
be cap sensitive, and is used to intensify an explosive reaction 
but which does not contain a detonator. Although a primer is 
generally thought of as containing a blasting cap, the primer 
cartridge may also be detonated by a downline of detonating 
cord. 

The possible undesirable effect of the cord on blasting 
agents, described in the "Detonating Cord Initiation" section, 
must be considered. If the column charge is cap sensitive, 
detonating cord will cause initiation to proceed from the top 



down. The manufacturer should be consulted to determine the 
minimum strength detonating cord that will reliably initiate a 
specific type of primer. Most cast phmers require a detonating 
cord strength greater than 25 gr/ft for reliable initiation. 



TYPES OF 
EXPLOSIVE USED 

The primer should have a higher detonation velocity than 
that of the column charge being primed. Some experts feel 
that priming efficiency continues to increase as the primer's 



44 



detonation velocity increases. In blastholes of 3-in diameter 
and less, cartridged dynamites and cap-sensitive cartridged 
slurries are commonly used as primers. For maximum efficiency, 
the diameter of the cartridge of explosive should be as near to 
the blasthole diameter as can be conveniently loaded. Gelatin 
dynamites are preferred over granular types because of their 
higher density, velocity, and water resistance. Some granular 
dynamites may be desensitized when subjected to prolonged 
exposure to water or to the fuel oil in AN-FO. Cast primers (fig. 
1 1 ) may be used if the borehole is large enough to accommo- 
date them. Small units of explosive that fit directly over the 
shell of a blasting cap can be used for priming bulk blasting 
agents in small-diameter holes. In some situations, where 



boreholes are dependably dry, a high-strength cap alone has 
been used to prime a bulk-loaded AN-FO in a small-diameter 
hole. However, it is strongly recommended that a small booster 
fitting directly over the shell of the cap be used rather than a 
high-strength blasting cap alone. The cap manufacturer should 
be consulted for a recommendation if you are in doubt. 

In larger diameter blastholes, cast primers are predomi- 
nately used, although some operators prefer to use cartridged 
high explosives. Ideally, the primer should fill the diameter of 
the blasthole as nearly as possible. However, primers are 
relatively expensive in comparison to the blasting agents used 
in larger boreholes, so economics are a factor in primer choice. 

AH blasting agents are subject to transient detonation veloci- 







Figure 48.— Highly aluminized AN-FO booster. (Courtesy Gulf on Chemicals co.) 



45 



ties (4, 6). That is. they may begin detonating at a relatively low 
velocity at the point of initiation with the velocity rapidly build- 
ing up until the blasting agent reaches its stable velocity, 
called the steady state velocity. This buildup occurs within 
about three charge diameters. A low initial velocity probably 
causes some loss of energy at the primer location. Low initial 
velocities can result when the primer is too small or of inade- 
quate strength, or when the blasting agent is poorly mixed or 
partially desensitized by water. 

In large-diameter slurry columns, a 1-lb cast primer or a 
cartridge of gelatin dynamite is often an adequate primer. In 
AN-FO columns where conditions are dependably dry, a 1 -lb 
primer is sometimes adequate. However, where dampness 
exists, or where low transient velocities are a particular concem, 
it is recommended that a 25- or 50-lb charge of high-energy 
slurry or aluminized AN-FO be poured around the phmer. This 
is called combination priming. High detonation pressure slur- 
ries (12-13) and highly aluminized products (9) have been 
recommended as combination primers (fig. 48). Bureau of 
Mines research (4) indicates that each type of product does a 
good job of raising the velocity in the transient zone. An added 
benefit of combination priming is the margin of safety in damp 
boreholes that may partially desensitize AN-FO. 

Cast primers have been developed which incorporate an 
internal millisecond delay. The cast primers and the delay 
devices are supplied separately, with directions for assembly 
(fig. 12). These delay primers are slipped onto a detonating 
cord downline and are especially useful in providing multiple 
delays in the blasthole on a single downline. 



PRIMER 
MAKEUP 

Proper care and technique in making primers is very impor- 
tant because this is the time in the blasting process at which 
the sensitive initiator and the powerful explosive cartridge are 
first combined. Because of the additional hazard involved, 
primers should be made up as close to the blast site as 
practical and immediately before loading. 

In large tunnel projects, it is generally agreed that an outside 
primer makeup facility is best, assuming that transportation 
from the facility to the working face is safeguarded. Primers 
should be dismantled before removal from the blasting site. An 
adequate hole must be punched into the cartridge to insure the 
detonator can be fully imbedded. Care must be taken to assure 
that the detonator does not come out of the primer cartridge 
during loading. The primer cartridge should never be tamped 
or dropped down the borehole. One or more cartridges or a 
few feet of AN-FO should be placed above the primer cartridge 
before dropping or tamping begins. 

In small-diameter holes, it is especially important that the 
end of the cap points in the direction of the main charge. It is 
also strongly recommended in small-diameter holes that the 
primer cartridge be the first cartridge placed into the blasthole. 
When priming small-diameter cartridges, the hole for the deto- 
nator is usually punched in the end of the cartridge. With 
electric caps, the wires are usually half hitched around the 
cartridge (fig. 49). Two half hitches are commonly used. The 
tubes or fuse from nonelectric detonators are not half hitched. 
It is recommended that the tubes or fuse be taped to the 
cartridge to assure that the cap is not pulled out during loading. 

Some safety fuse will not stand the sharp bend required for 
end priming. In this case, a diagonal hole is punched all the 
way through the cartridge and a second diagonal hole is 
punched partially through. The cap and fuse is strung through 



Electric 
blasting 




Half hitch 



Leg wires 
Figure 49.— Cartridge primed with electric blasting cap. 



the first hole, placed into the second hole, and pulled secure. 
Here again, taping of the fuse to the cartridge will assure that 
the cap is not pulled out during loading. 

When attaching detonating cord directly to the small-diameter 
primer cartridge, the detonating cord is usually inserted into a 
deep axial hole in the end of the cartridge. The cord is then 
either taped to the cartridge, passed through a diagonal hole in 
the cartridge, or secured with a half hitch to assure that the 
cord will not pull out. 

When priming large-diameter cartridges with electric blast- 
ing caps, a diagonal hole is punched from the top center of the 
cartridge and out the side about 8 in from the top. The cap 
wires are doubled over, threaded through the hole, and wrapped 
around the cartridge. The cap is placed into a hole punched 
into the top of the cartridge and the assembly is pulled tight. 
Tape may be used for extra security. 

Detonating cord is secured to large-diameter cartridges by 
punching a diametrical hole through the cartridge, passing the 
cord through the cartridge, and tying the cord at the top of the 
cartridge with a secure knot. This should not be done when 
using non-water-resistant explosive products in wet boreholes 



46 



because me cartridge may become desensitized by water 
entering the punched hole. Cap and fuse is not commonly 
used with large cartridges. With other nonelectric initiators, it is 
recommended that cast primers rather than large-diameter 
explosive cartridges be used. 

Cast primers (fig. 11) are most commonly used to prime 
large-diameter blastholes. For use with detonating cord, a 
cast primer with a single axial hole is used. The cord is passed 
thorugh the cord "tunnel" and tightly knotted at the bottom of 
the primer. Since this knot will not pull back through the tunnel 
it is not necessary to tie the cord around the primer. Subse- 
quent primers can be added wherever desired by passing the 
downline at the blasthole collar through the primer tunnel and 
sliding the primer down the downline. Placement of delay cast 
primers on the downline is done in a similar fashion except that 
the tunnel for the cord is connected to the perimeter of the 
primer rather than passing through the center of the primer 
itself. 

Cast primers for use with detonators have a cap well in 
addition to a tunnel. The cap is inserted through the tunnel and 
back up into the well, making sure that the cap is seated in the 
bottom of the well (fig. 50). Although the cap will usually stay 
securely in the primer using this type of configuration, it is a 
good idea to use a wrap of tape around the end containing the 



cap well for security. Remember that not all cast primers have 
tunnels large enough to accept the Hercudet duplex tubing. 



PRIMER 
LOCATION 

Proper location of the primer is important from the stand- 
point of both safety and efficiency (1, 6). When using cartridged 
products in small-diameter blastholes, the primer should be 
the first cartridge placed into the hole, with the cap pointing 
toward the collar. This assures maximum confinement and the 
most efficient use of the explosive's energy. Placing the primer 
in the bottom minimizes bootlegs and also protects against 
leaving undetonated explosives in the bottom of the hole if the 
cartridges become separated. The primer cartridge must not 
be cut, deformed, or tamped. If bulk products are being loaded, 
the primer may be raised slightly from the bottom of the hole. 

In bench blasting with a bulk loaded product, where subdrilling 
is used, the primer should be placed at toe level, rather than in 
the bottom of the hole, to reduce ground vibrations. If there is 
some compelling reason to place the primer at the collar of the 
hole the detonator should be pointed toward the bottom of the 
hole. 





m.^ 



Figure 50.— Priming cast primer with electric blasting cap. (Courtesy Austin Powder Co.) 



47 



In large-diameter blastholes, the location of the primer is 
more a matter of choice, although bottom initiation is recom- 
mended to maximize confinement of the charge. To help 
reduce vibrations, the primer should be at toe level rather than 
in the bottom of the hole, where subdrilling is used. Bottom- 
initiated holes tend to produce less flyrock and airblast than 
top-initiated holes, assuming that all other blast dimensions 
are equal. If pulling the toe is not a significant problem, some 
operators prefer to place the primer near the center of the 
charge. This gives the quickest total reaction of the explosive 
column and may yield improved fragmentation. Top priming is 
seldom recommended except where the only fragmentation 
difficulty is a hard band of rock in the upper portion of the 
bench. A rule of thumb, when using a single primer in a large- 
diameter blasthole, is to place the primer in the zone of most 
difficult breakage. This will normally be the toe area. Figure 51 
summarizes some desirable and undesirable locations for 
primers in large-diameter blastholes. 



ffl: 




pdmmg pnn 
I lurblail,! (mi 
llyioct) 



Figure 51.— Priming blasting agents in large-diameter 
blastholes. 



MULTIPLE PRIMING 

In many blasting situations, single-point priming may be 
adequate. However, there are some situations in which multi- 
ple primers in a single borehole may be needed. The first is 
where deck charges are used. Deck charges are used (1) to 
reduce the powder factor in a blast while still maintaining 
satisfactory powder distribution, (2) to break up boulder-prone 
caprock in the stemming area of the blast, or (3) to reduce the 
charge weight per delay to reduce vibrations. In situation 3, 
each deck in the hole is on a different delay period. In 1 and 2, 
the decks within a single hole may be on the same or on 
different delays. In any case, each deck charge requires a 
separate primer. Some States, such as Pennsylvania, require 
at least two primers per blasthole. 

The second reason for multiple priming is as a safety factor 
to assure total column detonation. With modern explosives 
and blasting agents, once detonation has been established it 
will proceed efficiently through the entire powder column. 
However, an offset in the powder column (fig. 34) may occur 
before detonation and cause part of the column not to propagate. 
This is most likely to occur with very long, thin charges or 
where slip planes are present in the burden area. In these 
cases, two or more primers should be spaced throughout the 
powder column. Frequently, these primers will be on the same 
delay. Where single point priming is preferred, but one or more 
additional primers are needed to assure total column propagation, 
the additional primers are put on a later delay period. 

With multiple delayed decks in a blasthole, detonation should 
proceed from the bottom up where a good free face exists. 
Where the shot is tight, such as in area coal mining, detonation 
from the top down will give some relief to the lower decks. 

Axial priming, which employs a central core of primerthrough- 
out an AN-FO column, has been used successfully but appears 
to have no particular advantage over single point or multiple 
point priming. Axial priming is more expensive than conven- 
tional priming. 



REFERENCES 



1 . Ash, R. L. The Mechanics of Rock Breakage, Parts 1, 11, III, and 
IV. Pit and Quarry, v. 56, No. 2, August 1963, pp. 98-112; No. 3, 
September 1 963, pp. 11 8-1 23; No. 4, October 1 963, pp. 1 26-1 31 ; No. 
5, November 1 963, pp. 1 09-1 1 1 , 1 1 4-1 1 8. 

2. Atlas Powder Co. (Dallas, TX). Handbook of Electric Blasting. 
Rev. 1976, 93 pp. 

3. Chlronis, N. P. New Blasting Machine Permits Custom- 
Programmed Blast Patterns. Coal Age, v. 79, No. 3, March 1974, pp. 
78-82. 

4. Condon, J. L., and J. J. Snodgrass. Effects of Primer Type and 
Borehole Diameter on AN-FO Detonation Velocities. Min. Cong. J., v. 
60, No. 6, June 1974, pp. 46-47, 50-52. 

5. Dick, R. A. New Nonelectric Explosive Initiation Systems. Pit & 
Quarry, v. 68, No. 9, March 1976, pp. 104-106. 

6. . Puzzled About Primers for Large Diameter AN-FO 

Charges? Here's Some Help to End the Mystery. Coal Age, v. 81 , No. 
8, August 1976, pp. 102-107. 

7. E. I. du Pont de Nemours & Co., Inc. (Wilmington, DE). Blaster's 
Handbook. 16th ed., 1978, 494 pp. 

8. Ensign BIckford Co. (SImsbury, CN). Primacord Detonating Cord. 
9th printing, copyright 1963, 68 pp. 



9. Grant, C. H. Metallized Slurry Boosting: What It Is and How It 
Works. Coal Age, v. 71 , No. 4, April 1966, pp. 90-91 . 

10. Hagan, T. N. Optimum Priming for Ammonium Nitrate Fuel-Oil 
Type Explosives. Proc. Southern and Central Queensland Conf. of 
the Australasian Inst, of Min. and Met., Parkville, Australia, July 1974, 
pp. 283-297; available for consultation at Bureau of Mines Twin Cities 
Research Center, Minneapolis, MN. 

1 1 . Institute of Makers of Explosives Safety Library (Washington, 
DC). Safety Guide for the Prevention of Radio Frequency Radiation 
Hazards in the Use of Electric Blasting Caps. Pub. No. 20, October 
1978,20 pp. 

12. Junk, N. M. Overburden Blasting Takes on New Dimensions. 
Coal Age, v. 77, No. 1 , January 1972, pp. 92-96. 

13. Research on Primers for Blasting Agents. Min. Cong. 

J., v. 50, No. 4, April 1964, pp. 98-101. 

14. Sengupta, D., G. French, M. Heydari, and K. Hanna. The 
Impact of Eliminating Safety Fuse From Metal/Nonmetal Mines (Con- 
tract J029501 0, Scl. Applications, Inc.). BuMlnesOFR 61-81, August 
1980, 21 pp.; NTIS PB 81-214386. 



49 



Chapter 3.— BLASTHOLE LOADING 



Blasthole loading involves placing all of the necessary ingredi- 
ents into the blasthole, including the main explosive charge, 
deck charges, initiation systems, primers, and stemming. 
Blasthole loading techniques vary depending on borehole 
diameter, type of explosive, and size of the blast. For the 
purpose of this discussion, boreholes have been arbitrarily 
classified as small diameter (<4 in) and large diameter 
(>4 in). Small-diameter boreholes may be drilled at practi- 



cally any inclination from vertically down to vertically up. Large- 
diameter blastholes are usually drilled vertically down, but in 
some cases are angled or horizontal. 

As a specific precaution, blastholes should never be loaded 
during the approach or progress of an electrical storm. Gen- 
eral descriptions of blasthole loading procedures are in the 
literature f2-5;.^ 



CHECKING THE BLASTHOLE 



Before loading begins, the blastholes should be checked. 
Depending on the designed depth, either a weighted tape 
measure or a tamping pole should be used to check that the 
boreholes are at the proper depth. If a hole is deeper than the 
plan calls for, drill cuttings or other stemming material should 
be used to bring the bottom of the hole up to the proper level. 
Loading an excessively deep blasthole is a waste of explosive 
and usually increases ground vibrations. Boreholes that are 
less than the planned depth should either be cleaned out with 
the drill or compressed air, or redrilled. Sometimes economics 
or equipment limitations may dictate that a shot be fired with a 
few short holes. The blasting foreman should make this decision. 

Occasionally a borehole may become obstructed. On a 
sunny day, a mirror may be used to check for obstructions. 
Obstructions in small holes may sometimes be dislodged with 
a tamping pole. In large, vertical holes, a heavy weight sus- 
pended on a rope and dropped repeatedly on the obstruction 
may clear the hole. It may be necessary to use the drill string to 
clear a difficult obstruction or, if the obstruction cannot be 
cleared, redrilling may be necessary. 

If it is necessary to redrill a hole adjacent to a blocked hole, 
the blocked hole should be filled with stemming. If this is not 
done, the new hole may shoot into the blocked hole and vent, 
causing excessive flyrock, airblast, and poor fragmentation. A 
hole must not be redrilled where there is a danger of intersect- 
ingajoaded hole. 

While checking the hole for proper depth, it is convenient to 
check for water in the borehole. With just a little experience, 
the blaster can closely estimate the level of water in a borehole 
by visually checking the tamping pole or weighted tape for 
wetness after the borehole depth check has been made. To 
get a more accurate check, the weighted end of the tape can 
be jiggled up and down at the water level. A splashing sound 
will indicate when the weight is at the water level. 

A blasthole may pass through or bottom into an opening. 
Where this opening is not unduly large, it may be filled with 





F5T^ S..m 



Figure 52. — Corrective measures for voids. 

stemming material (fig. 52). Where the opening is too large for 
this to be practical, the hole must either be left unloaded, 
redrilled in a nearby location, or plugged. 

A simple method for plugging a blasthole is as follows. A 
stick is tied to the end of a rope, lowered into the void, and 
pulled back up so it lodges crosswise across the hole. The 
rope is staked securely at the borehole collar. Bulky materials 
such as empty powder bags or rags are then dropped down 
the hole, dirt is then shoveled down the hole to form a solid 
bottom, after which explosive loading can proceed. Where 
voids are commonplace, you may want to develop a tailormade 
borehole plugging device. 

In some districts hot holes may be encountered, although 
this is not very common. Hot holes may occur in anthracite 
mining or other areas of in situ coal seam fires. If there is 
reason to suspect a hot hole, the hole can be checked by 
suspending a thermometer in it for a few minutes. Explosive 
materials should not be loaded into holes hotter than 1 50° F. 



GENERAL LOADING PROCEDURES 



Blastholes may be loaded with bulk or packaged products. 
Bulk products are either poured into the hole, augered, pumped, 
or blown through a loading hose. Packaged products are 
either dropped into the hole, pushed in with a tamping pole or 
other loading device, or loaded through a pneumatic tube. It is 



a good idea to check the rise of the powder column frequently 
as loading progresses, using a tamping pole, weighted tape, 



' Italicized numbers in parentheses refer to items in the list of refer- 
ences at the end of this chapter. 



50 



or loading hose. This will give warning of a cavity or oversized 
hole that is causing a serious overcharge of explosive to be 
loaded, and will also assure that sufficient room is left at the 
top of the hole for the proper amount of stemming. When the 
powder column has reached the proper location, the primer is 
loaded into the borehole. It is important that the wires, tubes, 
or detonating cord leading from the primer are properly secured 
at the borehole collar in vertical or nearly vertical holes, using a 
rock or stake. 

in almost all situations it is recommended that the explosive 
charge be totally coupled. Total coupling means that the charge 
completely fills the borehole diameter. Bulk loading of explo- 
sives assures good coupling. When cartridged products are 
used, coupling is improved by slitting the cartridges and tamp- 
ing them firmly into place. There are four situations where 
cartridges or packages of explosives should not be tamped. 

1 . In permissible coal mine blasting, where deforming the 
cartridge is against regulations. 

2. In controlled blasting, where string loads or even gaps 
between cartridges are used to reduce the charge load in the 
perimeter holes to prevent shattering. 

3. In water, where the package serves as protection for a 
non-water-resistant explosive product. 

4. A primed cartridge is never tamped. 

It is recommended that all blastholes be stemmed to improve 
the efficiency of the explosive and to reduce airblast and 
flyrock. As a rule of thumb, the length of stemming should be 
from 14 to 28 times the borehole diameter. Sized crushed 



stone makes the most efficient stemming. However, for rea- 
sons of economy and convenience, drill cuttings are most 
commonly used. Large rocks should never be used as stem- 
ming as they could become a dangerous source of flyrock and 
may also damage the wires, cord, or tubes of the initiation 
system. Because it is inconvenient to stem horizontal holes, 
horizontal rounds are sometimes left unstemmed, although it 
is recommended that all blastholes be stemmed to improve 
blasting efficiency. By regulation, underground coal mine rounds 
must be stemmed with noncombustible stemming such as 
waterfilled cartridges or clay "dummies." 

Care must be exercised in using detonating cord downlines 
in relatively small blastholes. See "Field Application" in the 
"Detonating Cord Initiation" section of chapter 2 for recom- 
mended grain loads of detonating cord as a function of blasthole 
diameter. 

One solution to blasting in wet boreholes is to use a water- 
resistant explosive. However, economics often favor dewater- 
ing the blasthole and loading it with AN-FO inside a protective 
plastic borehole liner. Although dewatering has been used 
mostly in large-diameter holes, it can be used in diameters 
below 4 in. To dewater, a pump is lowered to the bottom of the 
hole. When the water has been removed, the hole is lined with 
a plastic sleeve as follows. A roil of hollow plastic tubing is 
brought to the collar of the hole. A rock is placed inside the end 
of the tubing and a knot is tied in the end of the tubing to hold 
the rock in place. The tubing is reeled into the borehole, and 
care is taken not to tear it. The tubing is cut off at the collar, 
allowing 4 to 6 ft extra for charge settlement. The AN-FO and 
primer are loaded inside the tubing and the hole is stemmed. 
Where water is seeping into the borehole, it is important that 
the tubing and AN-FO be loaded quickly to prevent the hole 
from refilling with water. 



SMALL-DIAMETER BLASTHOLES 



When small-diameter blastholes are loaded, the primer car- 
tridge is normally loaded at the bottom of the hole. This gives 
maximum confinement at the point of initiation and also guards 
against leaving undetonated explosive in the bottom of the 
borehole if it should become plugged during loading or cut off 
during the blasting process. Some experts condone, or even 
recommend a cushion stick or two, but the general recommen- 
dation is not to use a cushion stick. To avoid having the 
detonator fall out of the primer cartridge, the cartridge should 
never be slit, rolled, or othenvise deformed. The primer car- 
tridge should never be tamped. 



CARTRIDGED 
PRODUCTS 

Cartridged dynamites and slurries (water gels) are com- 
monly used in small-diameter blastholes. These cartridges 
are usually slit, loaded by hand, and tamped to provide maxi- 
mum coupling and loading density. One or two cartridges 
should' be loaded after the primer before tamping begins. 
Tamping should be done firmly, but not excessively. Using the 
largest diameter cartridge compatible with the borehole diame- 
ter will increase coupling and loading density. 

Pneumatic systems for loading water gel cartridges are 
available. The cartridges are propelled through a loading hose 
at high velocity at a rate of up to one cartridge per second. The 
cartridges are automatically slit as they enter the blasthole and 



each cartridge splits upon impact. Because of the high impact 
imparted to the cartridges, loading dynamites with this type of 
loading system is not permitted. Pneumatic cartridge loaders 
are especially useful in loading holes that have been drilled 
upward. 



BULK DRY 
BLASTING AGENTS 

Bulk dry blasting agents, usually AN-FO, may be loaded into 
small-diameter blastholes by pouring from a bag or by pneu- 
matic loading through a loading hose (fig. 53). Poured charges 
in diameters less than 4 in lose some efficiency because of 
AN-FO's low density and its reduced detonation velocity at 
small diameters. As with all bulk loading, good coupling is 
achieved. Caution should be exercised in using poured AN-FO 
charges in diameters less than 2 in. This should be done only 
under bone-dry conditions because AN-FO's efficiency begins 
to drop significantly at this point, and water will compound the 
problem. 

Pneumatic loading of AN-FO in small holes is recommended 
because of ease of handling, faster loading rates, and the 
improved performance of the AN-FO caused by partial pulver- 
izing of the prills, which gives a higher loading density and 
greater sensitivity (1, 4). The two basic types of pneumatic 
loading systems are the pressure vessel and the ejector or 
venturi-type loader. 



51 




Figure 53.— Pneumatic loading of AN-FO underground. (Courtesy Hercules inc.) 



A pressure vessel type AN-FO loader should have a pres- 
sure regulator so that the tank pressure does not exceed the 
manufacturer's recommendation, usually 30 psi. This low- 
pressure type loader propels the prills into the borehole at a 
low velocity and high volume rate, loading the AN-FO at a 
density slightly above its poured density with a minimum amount 
of prill breakage. In a pressure vessel, the compartment con- 
taining the AN-FO is under pressure during loading. Loading 
rates of over 1 00 Ib/min can be achieved with some equipment 
and pressure vessels with AN-FO capacities of 1 ,000 lb are 
available. The smaller and more portable pressure vessel 
loaders have loading rates of 15 to 50 Ib/min and AN-FO 
capacities of 75 to 200 lb. Pressure vessels larger than 1 cu ft 
in volume should meet ASME specifications for construction. 

The ejector-type system (fig. 54) uses the venturi principle 
to draw AN-FO from the bottom of an open vessel and propel it 
at a high velocity but low volume rate into the borehole, pulveriz- 
ing the prills and giving bulk loading densities near 1.00. 
Ejector systems operate from line pressures of 40 to 80 psi 
and load at rates of 7 to 10 Ib/min. Combination loaders are 
available that force feed a venturi from a pressurized pot. This 
system gives the same high loading density and prill breakage 
as the straight venturi loader with an increase in loading rate. 
Specifications of pneumatic loading systems are given in table 
3. The detonation velocity of AN-FO as a function of charge 




Semiconductive 
hose 



Figure 54.— Ejector-type pneumatic AN-FO loader. 



52 



Table 3 - Characteristics of pneumatically loaded AN-FO 
in small-diameter blastholes 



Loading 
device 


Tank 

presure, 

psi 


Jet 

pressure, 

psi 


Loading 
rate,' 
Ib/min 


Loading 
density, 
g/cu cm 




10-30 
NAp 
20 


NAp 
40-80 
20-80 


15-70 
7-10 
15-25 


0.80-0.85 


Ejector loader Qet) 

Combination loader.... 


.90-1.00 
.90-1 .00 


NAp Not applicable. 


^Varies with hose diameter 







diameter for poured and pneumatically loaded charges is 
shown in figure 55. The benefits of high-velocity pneumatic 
loading are significant at small borehole diameters. 

A problem may arise where a high-pressure ejector loader 
is used to load AN-FO in small holes in soft formations such as 
uranium ore. The pulverized prills may be dead pressed by the 
compression from adjacent charges fired on earlier delays. 
This can cause the AN-FO not to fire. 

Static electricity can be a hazard when loading AN-FO 
pneumatically into small-diameter boreholes. Static electhcity 
hazards can be reduced by using antistatic caps or nonelectric 
initiators such as Hercudet, Nonel, or Detaline. A semiconductive 
hose with a minimum resistance of 1 ,000 ohms/ft and 1 0,000 
ohms total resistance, and a maximum total resistance of 
2,000,000 ohms for the entire system, should be used. The 
pneumatic loader should be properly grounded. 

Homemade loading equipment should not be used. All equip- 
ment should be operated at the proper pressure. Gaps in the 
powder column can be avoided by keeping the hopper full and 
maintaining a constant standoff distance between the end of 
the loading hose and the column of AN-FO. Loading profi- 
ciency improves through operator experience. 



Pneumatically 
lq/cucm,_— loaded charges 




CHARGE DIAMETER, 



Figure 55.— AN-FO detonation velocity as a function 
of charge diameter and density. 



The pneumatic loading tube is useful for blowing standing 
drill water from a horizontal borehole. However, if the borehole 
is "making water," external protection for the AN-FO by means 
of a plastic sleeve is required. Loading inside a plastic bore- 
hole sleeve is not recommended for underground work because 
of the static electricity hazard during loading and toxic fumes 
generated during blasting. If plastic-sleeve protection with 
pneumatic loading in well-ventilated locations is required, a 
nonelectric detonating system should be used because the 
insulating effect of the sleeve is likely to cause a buildup of 
static electricity. 

BULK SLURRIES 

Slurries may be bulk loaded into blasthole diameters as 
small as 2 in. These products are frequently poured from bags 
(fig. 56), but occasionally bulk pumping units are used (fig. 57). 
The sensitivity of slurhes, and hence the diameter at which 
they may be effectively used, depends largely on their 
formulation. The use of bulk slurries in diameters below those 
intended for the product can result in substandard blasts or 
misfires. The manufacturer should be consulted when loading 
bulk slurries into small-diameter blastholes. 



PERMISSIBLE 
BLASTING 

Loading blastholes in underground coal mines is strictly 
regulated by MSHA in order to prevent ignition of explosive 
atmospheres. Only permissible explosives may be used in 
underground coal mines. Certain nitroglycerin-based explosives, 
emulsions, slurries, and water gels have been certified as 
permissible by MSHA (6). 

The primer plus the remaining cartridges are stringloaded 
and pushed back into the hole as a single unit to avoid getting 
coal dust between the cartridges. Charge weights may not 
exceed 3 lb per borehole. Black powder, detonating cord, and 
AN-FO are not permissible. Blastholes are initiated with cop- 
per alloy shell electric blasting caps. All holes must be stemmed 
with noncombustible material such as water bags or clay 
dummies. The stemming length must be at least 24 in or 
one-half the depth of the borehole, whichever is less. Addi- 
tional rules for permissible blasting are given in the "Blast 
Design" chapter. Permissible blasting procedures are also 
required for gassy noncoal mines, but are frequently less 
sthngent than for coal mines. 



With few exceptions, economics and efficiency favor the 
use of bulk loading in blasthole diameters larger than 4 in. The 
products are cheaper, loading is faster, and the well-coupled 
bulk charge gives better blasting efficiency. As described in 
the "Priming" section of chapter 2, large-diameter blastholes 
may be top, center, or toe primed, or multiple primers may be 
used. 



^Reference to specific trade names does not imply endorsement by 
the Bureau of Mines. 



LARGE-DIAMETER BLASTHOLES 

PACKAGED PRODUCTS 



1 



Large-diameter dynamite cartridges are seldom used today 
except for occasional use as primers. AN-FO and slurries give 
better economy in large-diameter blastholes. When wet bore- 
holes are encountered, and the operator wants to use AN-FO, 
water-resistant polyburlap packages of partially pulverized, 
densified AN-FO are used (fig. 7). Densification is necessary 
so that the packages will sink in water. AN-FO packages 
should be carefully lowered into water-filled holes rather than 
dropped, because a broken bag will result in desensitized 
AN-FO, an interruption in the powder column and, most likely. 




Figure 56. — Pouring siurry into smail-diameter l>oreliole. (Courtesy Atlas Powder co.) 



some unfired AN-FO. A disadvantage of waterproof AN-FO 
packages is that some borehole coupling is lost. Also the heat 
lost to the water will reduce the energy released. Where it is 
desired to use AN-FO in wet boreholes, the option of borehole 
dewatering should be investigated. 

Slurries are available in polyethylene packaging in diame- 
ters up to 8 in (fig. 10). Some of these products are semirigid 
and others are in dimensionless bags that will slump to fit the 
borehole diameter. With the semirigid cartridges, the advan- 
tage of borehole coupling is lost. 



BULK DRY 
BLASTiNG AGENTS 

Bulk loading offers significant advantages over loading of 
packaged products in large-diameter blastholes, including 
cheaper products, faster loading, and better use of the avail- 
able space in the borehole. 

The bulk AN-FO or prills are stored in overhead storage 
bins, from which they are loaded into the bulk trucks. The 
AN-FO may be trucked to the blast site in premixed form or the 
oil may be metered into the prills as they are placed into the 



blasthole. Bulk loading systems for dry blasting agents (AN-FO) 
may be of the auger or pneumatic type. 

Auger loading gives the fastest loading rates. A side-boom 
auger is satisfactory for loading one row of holes at a time. 
Where it is desired to reach more holes from one setup, an 
overhead-boom auger with a 350° radius of swing can be 
used. With this type of equipment, flexible tubing usually extends 
from the end of the auger boom to ground level. The amount of 
blasting agent delivered into the blasthole is sometimes indi- 
cated on a meter in the truck. In other situations a hopper with 
a given volume of capacity is hung at the end of the auger 
boom to measure the AN-FO as it is loaded. Bulk loading 
trucks have capacities of from 2,000 to 30,000 lb of AN-FO, 
and with auger systems can deliver up to 600 lb of AN-FO per 
minute into a blasthole. 

Pneumatic loading is also used in large-diameter boreholes. 
Pneumatic units are especially useful in rough terrain, where a 
long loading hose is used to load numerous blastholes from a 
single setup. 

Hand pouring AN-FO from 50-lb bags is still practiced at 
operations where the capital expense of a bulk system cannot 
be justified. This, of course gives the same complete coupling 
as bulk loading. 



54 




Figure 57. — Pumping slurry into small-diameter borehole. (Courtesy Ou Pont Co.) 



BULK SLURRIES 

Bulk slurry pumping is commonplace in large-diameter vertical- 
hole blasting. Some slurry trucks have capacities of up to 
30,000 lb of slurry and have typical pumping rates of 200 to 
400 Ib/min. A bulk slurry truck may bring a plant-mixed 
slurry to the borehole or it may carry separate ingredients for 
onsite mixing. 

Onsite slurry mixing is more complex than AN-FO mixing 
and is usually done by a competent explosive distributor rather 
than the consumer. Plant mixing permits closer quality control 
in the blending of ingredients, whereas onsite mixing permits 



different energy densities to be loaded from hole to hole or in 
different locations within a single hole. 

The slurry is pumped as a liquid (fig. 58) and a cross-linking 
ingredient is added just as the slurry enters the loading hose. 
Cross linking to a gelatinous consistency begins in the hose 
and is completed in the borehole. A meter on the bulk truck 
indicates the amount of slurry that has been loaded. 

Hand pouring of slurry from polyethelene packages (fig. 56) 
is still practiced at operations where the volume of slurry used 
does not justify a bulk-loading truck. Pouring, rather than 
loading the entire package, gives complete borehole coupling. 



55 




Figure 58.— Slurry leaving end of loading hose. (Courtesy du Pont co.) 



REFERENCES 



1. Atlas Powder Co. (Dallas, TX). Pneumatic Loading of Nitro- 
Cart)o-Nitrates; Static Electricity, Fumes, and Safe Handling. Undated, 
17 pp. 

2. Dannenberg, J. How To Solve Blasting Materials Handling 
Problems. Rock Products, v. 74, No. 9, September 1971, pp. 63-65. 

3. Dick, H. A. Explosives and Borehole Loading. Subsection 1 1 .7, 
SME Mining Engineering Handbook, ed. by A. B. Cummins and I. A. 
Given. Society of Mining Engineers of the American Institute of Mining, 
Metallurgical, and Petroleum Engineers, Inc., New York, v. 1, 1973, 
pp. 11-78— 11-99. 



4. E. I. du Pont de Nemours & Co., Inc. (Wilmington, DE). Blaster's 
Handbook. 16th ed., 1978, 494 pp. 

5. Langefors, U., and B. A. Kihistrom. The Modern Technique of 
Rock Blasting. John Wiley & Sons, Inc., New York, 1963, 405 pp. 

6. U.S. Mine Enforcement and Safety Administration. Active List of 
Permissible Explosives and Blasting Devices Approved Before Dec. 
31, 1975. MESA Inf. Rep. 1046, 1976, 10 pp. 



57 



Chapter 4.— BLAST DESIGN 



Blast design is not a precise science. Because of the widely 
varying nature of rock, geologic structure, and explosives, it is 
impossible to set down a series of equations which will enable 
the blaster to design the ideal blast without some field testing. 
Tradeoffs must frequently be made in designing the best blast 
for a given situation. This chapter will describe the fundamen- 
tal concepts of blast design. These concepts are useful as a 
first approximation for blast design and also in troubleshooting 
the cause of a bad blast. Field testing is necessary to refine the 
individual blast dimensions. 

Throughout the blast design process, two overriding princi- 



ples must be kept in mind. (1) Explosives function best when 
there is a free face approximately parallel to the explosive 
column at the time of detonation and (2) there must be ade- 
quate space into which the broken rock can move and expand. 
Excessive confinement of explosives is the leading cause of 
poor blasting results such as backbreak, ground vibrations, 
airblast, unbroken toe, flyrock, and poor fragmentation. 

Many of the principles discussed in this section were first 
presented by Ash (2)'' and later reported by Pugleise (7) 
during a study of quarrying practices in this country. 



PROPERTIES AND GEOLOGY OF THE ROCK MASS 



The character of the rock mass is a critical variable affecting 
the design and results of a blast. The nature of rock is very 
qualitative and cannot be quantified numerically. Rock charac- 
ter often varies greatly from one part of a mine to another or 
from one end of a construction job to another. Decisions on 
explosive selection, blast design, and delay pattern must take 
firsthand knowledge of the rock mass into account. For this 
reason, the onsite blaster usually has a significant advantage 
over an outside consultant in designing a blast. Although the 
number of variations in the character of rock is practically 
infinite, a general discussion of the subject will be helpful. The 
Bureau has published a report (7) that discusses the effects of 
geology on blast design. 



CHARACTERIZING 
THE ROCK MASS 

The keys to characterizing the rock mass are a good geolo- 
gist and a good driller. The geologist concentrates on obtain- 
ing data from the rock surface. Jointing is probably the most 
significant geologic feature of the rock. The geologist should 
document the direction, severity, and spacing between the 
joint sets. In most sedimentary rocks there are at least three 
joint sets, one dominant and two less severe. The strike and 
dip of bedding planes are also documented by the geologist. 
The presence of major zones of weakness such as faults, 
open beds, solution cavities, or zones of incompetent rock or 
unconsolidated material are also determined. Samples of freshly 
broken rock can be used to determine the hardness and 
density of the rock. 

An Observant driller can be of great help in assessing rock 
variations that are not apparent from the surface. Slow pene- 
tration and excessive drill noise and vibration indicate a hard 
rock that will be difficult to break. Fast penetration and a quiet 
drill indicate a softer, more easily broken zone of rock. Total 
lack of resistance to penetration, accompanied by a lack of 
cuttings or return water or air, means that the drill has hit a void 
zone. Lack of cuttings or return water may also indicate the 
presence of an open bedding plane or other crack. A detailed 
drill log indicating the depth at which these various conditions 
exist can be very helpful to the person designing the blast. The 
driller should also document changes in the color or nature of 
the drill cuttings, which will tell the blaster the location of 
vahous beds in the formation. 



ROCK DENSITY 
AND HARDNESS 

Some amount of displacement is required to prepare a 
muckpile for efficient excavation. The density of the rock is a 
major factor in determining how much explosive is needed to 
displace a given volume of rock (powder factor). The burden-to- 
charge diameter ratio, which will be discussed in the next 
section, "Surface Blasting," varies with rock density, causing 
the change in powder factor. The average burden-to-charge- 
diameter ratio of 25 to 30 is for average density rocks such as 
limestone (2.5 to 2.8 g/cu cm), schist (2.6 to 2.8 g/cu cm), or 
porphyry (2.5 to 2.6 g/cu cm). Denser rocks such as basalt (2.9 
g/cu cm) and magnetite (4.9 to 5.2 g/cu cm) require smaller 
ratios (higher powder factors). Lighter materials such as some 
sandstones (2.0 to 2.6 g/cu cm) or bituminous coal (1 .2 to 1 .5 
g/cu cm) can be blasted with higher ratios (lower powder 
factors). 

The hardness or brittleness of rock can have a strong effect 
on blasting results. Soft rock is much more "forgiving" than 
hard rock. If soft rock is slightly underblasted, it will probably 
still be diggable. If soft rock is slightly overblasted, excessive 
violence will not usually occur. On the other hand, slight 
underblasting of hard rock will often result in a tight muckpile 
that is difficult to dig. Overblasting of hard rock is likely to 
cause excessive flyrock and airblast. Blast designs for hard 
rock, then, require closer control and tighter tolerances than 
those for soft rock. 



VOIDS AND 
INCOMPETENT ZONES 

Unforeseen voids and zones of weakness such as solution 
cavities, underground workings, mud seams, and faults are 
serious problems in blasting. Explosive energy always seeks 
the path of least resistance (fig. 59). Where the rock burden is 
composed of alternate zones of hard material and incompe- 
tent material or voids, the explosive energy will be vented 
through the incompetent zones, resulting in poor fragmentation. 
Depending on the orientation of the zones of weakness with 
respect to free faces, excessive violence in the form of airblast 

^ Italicized numbers In parentheses refer to items in the list of references at the 
end of this chapter. 



58 




Secondary Principal 
joint set^ joint set^ 



JMUl 



Figure 59. — Loss of explosive energy through zones 
of wealcness. 

and flyrock may occur. A particular problem occurs when the 
blasthole intersects a void zone. In this situation, unless partic- 
ular care is taken in loading the charge, the void will be loaded 
with a heavy concentration of explosive, resulting in excessive 
airblast and flyrock. 

If these voids and zones of weakness can be identified, 
steps can be taken during borehole loading to improve fragmenta- 
tion and avoid violence. The best tool for this is a good drill log. 
The depths of voids and incompetent zones encountered by 
the drill should be documented. The geologist can help by 
plotting the trends of mud seams and faults. When charging- 
the blasthole, inert stemming material, rather than explosives, 
should be loaded through these weak zones. Voids should be 
filled with stemming (fig. 52). Where this is impractical because 
of the size of the void, it may be necessary to block the hole 
just above the void before continuing the explosive column, as 
described in the "Checking the Blasthole" section of chapter 3. 

Where the condition of the borehole is in doubt, the rise of 
the powder column should be checked frequently as loading 
proceeds. If the column fails to rise as expected, there is 
probably a void. At this point a deck of inert stemming material 
should be loaded before powder loading continues. If the 
column rises more rapidly than expected, frequent checking 
will assure that adequate space is left for stemming. 

Alternate zones of competent and incompetent rock usually 
result in unacceptably blocky fragmentation. A higher powder 
factor will seldom correct this problem; it will merely cause the 
blocks to be displaced farther. Usually the best way to alleviate 
this situation is to use smaller blastholes with smaller blast 
pattern dimensions to get a better powder distribution. The 
explosive charges should be concentrated in the competent 
rock, with the incompetent zones being stemmed through 
wherever possible. 



Stoble perimeter 



Unstable 
perimeter 



z 



IZZ 



zrzz 



r-y^ 



Figure 60.— Effect of jointing on the stability of an 
excavation. 



Joints 




Figure 61.— Tight and open corners caused by jointing. 



JOINTING 

Jointing can have a pronounced effect on both fragmenta- 
tion and the stability of the perimeter of the excavation. Close 
jointing usually results in good fragmentation. However, widely 
spaced jointing, especially where the jointing is pronounced, 
often results in a very blocky muckpile because the joint planes 
tend to isolate large blocks in place. Where the fragmentation 
is unacceptable, the best solution is to use smaller blastholes 
with smaller blast pattern dimensions. This extra drilling and 
blasting expense will be more than justified by the savings in 
loading, hauling, and crushing costs and the savings in sec- 
ondary blasting. 

Where possible, the perimeter holes of a blast should be 
aligned with the principal joint sets. This will tend to produce a 
more stable excavation, whereas rows of holes perpendicular 
to a primary joint set will tend to produce a more ragged, 
unstable perimeter (fig. 60). Jointing will often determine how 
the corners at the back of the blast will break out. To minimize 
backbreak and violence, tight corners, shown in figure 61, 
should be avoided. The open corner at the left of the figure is 
preferable. Given the predominant jointing in figure 61 , more 
stable conditions will result if the first blast is opened at the far 
right and is designed so that the hole in the rear inside corner 
contains the highest numbered delay. 



BEDDING 

Bedding can also have an effect on both the fragmentation 
and the stability of the excavation perimeter. Open bedding 
planes or beds of weak material should be treated as zones of 
weakness. Stemming, rather than explosive, should be loaded 
into the borehole at the location of these zones as shown in 
figure 62. In a bed of hard material, it is often beneficial to load 
an explosive of higher density than is used in the remainder of 
the borehole. To break an isolated bed of hard material near 
the collar of the blasthole, a deck charge is recommended, as 
shown in figure 63, with the deck being fired on the same delay 
as the main charge or one delay later. Occasionally, satellite 



'/M Xi^iy^-jf 



i\^\fei(S 



)P*;E=(lcaite';^lfc=ll©i^ KEY 

■^ ISL'Sij Stemming 
[Q ^H Explosive 

i 
Si 





-Open bed 



^Weok 
material 




Figure 62.— Stemming tlirough weak material and 
beds. 



DECK CHARGE 



SATELLITE HOLE 





Figure 63.— Two methods of breaking a liard collar zone. 



Figure 64.— Effect of dipping beds on slope stability 
and potential toe problems. 



holes are used to help break a hard zone in the upper part of 
the burden. Satellite holes are short holes, usually smaller in 
diameter than the main blastholes, which are drilled between 
the main blastholes. 

A pronounced bedding plane is frequently a convenient 
location for the floor of the bench. It not only gives a smoother 
floor but also may reduce subdrilling requirements. 

Dipping beds frequently cause stability problems and diffi- 
culty in breaking the toe of the burden. When the beds dip into 
the excavation wall, the stability of the slope is enhanced (fig. 
64). However, when beds dip outward from the wall they form 
slip planes that increase the likelihood of slope deterioration. 
Blasthole cutoffs caused by differential bed movement are 
also more likely. Beds dipping outward from the final slope 
should be avoided wherever possible. 

Although beds dipping into the face improve slope stability, 
they do create toe problems (fig. 64), as the toe material tends 
to break out along the bedding planes. Dipping beds such as 
these require a tradeoff. Which is the more serious problem in 
the job at hand, a somewhat unstable slope or an uneven toe? 
In some cases advancing the opening perpendicular to the 
dipping beds may be a good compromise. 

Many blasting jobs encounter site-specific geologic condi- 
tions not covered in this general discussion. A good explo- 
sives engineer is constantly studying the geology of the rock 
mass and making every effort to use the geology to his or her 
advantage, or at least to minimize its unfavorable effects. 



SURFACE BLASTING 



BLASTHOLE 
DIAMETER 

The size of blasthole is the first consideration of any blast 
design. The blasthole diameter, along with the type of explo- 
sive being used and the type of rock being blasted, will deter- 



mine the burden. All other blast dimensions are a function of 
the burden. This discussion assumes that the blaster has the 
freedom to select the borehole size. In many operations one is 
limited to a specific size borehole based on available drilling 
equipment. 
Practical blasthole diameters for surface mining range from 



|«-50'- 







mi 



S9 



•-50'^ 



Blast area 


15,000 sq ft 


Blast area = 15,000 sq ft 


Borehole diameter 


20 in 


Borehole diameter =2 in 


Number of holes 


4 


Number of holes = 400 


otol borehole area 


1,256 sq in 


Total borehole area = 1,256 sq in 


Burden 


50 ft 


Burden = 5ft 


Spacing 


75 ft 


Spacing =7 5 ft 



Figure 65.— Effect of large and small blastholes on 
unit costs. 



2 to 17 in. As a general rule, large blasthole diameters yield 
low drilling and blasting costs because large holes are cheaper 
to drill per unit volume and less sensitive, cheaper blasting 
agents can be used in larger diameters. However, larger diam- 
eter blastholes also result in large burdens and spacings and 
collar distances and hence, they tend to give coarser 
fragmentation. Figure 65 (3) illustrates this comparison using 
2- and 20-in-diameter blastholes as an example. Pattern A 
contains four 20-in blastholes and pattern B contains 400 2-in 
blastholes. In all bench blasting operations some compromise 
between these two extremes is chosen. Each pattern repre- 
sents the same area of excavation, 1 5,000 sq ft, each involves 
approximately the same volume of blastholes, and each can 
be loaded with about the same weight of explosive. 

In a given rock formation, the four-hole pattern will give 
relatively low drilling and blasting costs. Drilling costs for the 
large blastholes will be low, a low-cost blasting agent will be 
used, and the cost of detonators will be minimal. However, in a 
difficult blasting situation, the broken material will be blocky 
and nonuniform in size, resulting in higher loading, hauling, 
and crushing costs as well as requiring more secondary 
breakage. Insufficient breakage at the toe may also result. 

On the other hand, the 400-hole pattern will yield high 
drilling and blasting costs. Small holes cost more to drill per 
unit volume, powder for small-diameter blastholes is usually 
more expensive, and the cost of detonators will be higher. 
However, the fragmentation will be finer and more uniform, 
resulting in lower loading, hauling, and crushing costs. Sec- 
ondary blasting and toe problems will be minimized. Size of 
equipment, subsequent processing required for the blasted 
material, and economics will dictate the type of fragmentation 
needed, and hence the size of blasthole to be used. 

Geologic structure is a major factor in determining blasthole 
diameter. Planes of weakness such as joints and beds, or 
zones of soft, incompetent rock tend to isolate large blocks of 
rock in the burden. The larger the blast pattern, the more likely 
these blocks are to be thrown unbroken into the muckpile. 




Figure 66. 
hole size. 



-Effect of jointing on selection of blast- 



Note that in the top pattern in figure 66 some of the blocks are 
not penetrated by a blasthole, whereas in the smaller bottom 
pattern all of the blocks contain at least one blasthole. Owing 
to the better explosives distribution, the bottom pattern will 
give better fragmentation. 

As more blasting operations are carried out near populated 
areas, environmental problems such as airblast and flyrock 
often occur because of an insufficient collar distance above 
the explosive charge. As the blasthole diameter increases, the 
collar distance required to prevent violence increases. The 
ratio of collar distance to blasthole diameter required to pre- 
vent violence varies from 14:1 to 28:1, depending on the 
relative densities and velocities of the explosive and rock, the 
physical condition of the rock, the type of stemming used, and 
the point of initiation. A larger collar distance is required where 
the sonic velocity of the rock exceeds the detonation velocity 
of the explosive or where the rock is heavily fractured or low in 
density. A top-initiated charge requires a larger collar distance 
than a bottom-initiated charge. As the collar distance increases, 
the powder distribution becomes poorer resulting in poorer 
fragmentation of the rock in the upper part of the bench. 

Ground vibrations are controlled by reducing the weight of 
explosive fired per delay interval. This is more easily done with 
small blastholes than with large blastholes. In many situations 
where an operator uses large-diameter blastholes near popu- 
lated areas, several delayed decks must be used within each 
hole to control vibrations. 

Large holes with large blast patterns are ideally suited to an 
operation with the following characteristics: A large volume of 
material to be moved; large loading, hauling, and crushing 
equipment; no requirement for fine, uniform fragmentation; an 
easily broken toe; few ground vibration or airblast problems 
(few nearby neighbors); and a relatively homogeneous, easily 
fragmented rock without excessive, widely spaced planes of 



61 



weakness or voids. Many blasting jobs, however, present 
constraints that require smaller blastholes. 

In the final analysis, the selection of blasthole size is based 
on economics. It is important to consider the economics of the 
overall excavation or mining system. Savings realized through 
indiscriminate cost cutting in the drilling and blasting program 
may well be lost through increased loading, hauling, and crush- 
ing costs and increased litigation costs owing to disgruntled 
neighbors. 



TYPES OF 
BLAST PATTERNS 

There are three commonly used drill patterns; square, 
rectangular, and staggered. The square drill pattern (fig. 67) 
has equal burdens and spacings, while the rectangular pattern 
has a larger spacing than burden. In both the square and 
rectangular patterns, the holes of each row are lined up directly 
behind the holes in the preceding row. In the staggered pattern 
(fig. 67), the holes in each row are positioned in the middle of 
the spacings of the holes in the preceding row. In the stag- 
gered pattern, the spacing should be larger than the burden. 

The staggered drilling pattern is used for row-on-row firing; 
that is, where the holes of one row are fired before the holes in 
the row immediately behind them as shown in figure 68. The 
square or rectangular drilling patterns are used for firing V-cut 
(fig. 69) or echelon rounds. Either side of the blast round in 
figure 69 by itself would be called an echelon blast round. In 
V-cut or echelon blast rounds the burdens and subsequent 
rock displacement are at an angle to the original free face. 
Looking at figure 69, with the burdens developed at a 45° 
angle with the original free face, you can see that the originally 
square drilling pattern has been transformed to a staggered 
blasting pattern with a spacing twice the burden. The simple 
patterns discussed here acount for the vast majority of the 
surface blasts fired. 



Square 



Rectangular Staggered 

I 

o o o I o o o 

o o I ° o o 

o o o I o o o . 

° I ° ° ° 



Figure 67.— Three basic types of drill pattern. 




•2-f 
oo 



Figure 68. — Corner cut staggered blast pattern- 
Simultaneous initiation within rows (blasthole spacing, 
S, is twice the burden, B). 




S = 2B 

Figure 69.— V-echelon blast round (true spacing, 
S, is twice the true burden, B). 



BURDEN 

Figure 70 is an isometric view showing the relationship of 
the various dimensions of a bench blast. The burden is defined 
as the distance from a blasthole to the nearest free face at the 
instant of detonation. In multiple row blasts, the burden for a 
blasthole is not necessarily measured in the direction of the 
original free face. One must take into account the free faces 
developed by blastholes fired on lower delay periods. As an 
example, in figure 68, where one entire row is blasted before 
the next row begins, the burden is measured in a perpendicu- 
lar direction between rows. However, in figure 69 the blast 
progresses in a V-shape. In this situation, the true burden on 
most of the holes is measured at an angle of 45° from the 
original free face, as shown in the figure. 

It is very important that the proper burden be calculated, 
taking into account the blasthole diameter, the relative density 




KEY 

B Burden 

J Subdrilling 

r Collar distance 

5 Spacing 

H Hole depth 



Figure 70.— Isometric view of a bench blast. 



62 



of the rock and the explosive, and to some degree, the length 
of the blasthole. An insufficient burden will cause excessive 
airblast and flyrock. Too large a burden will give inadequate 
fragmentation, toe problems, and excessive ground vibrations. 
Where it will be necessary to drill a round before the previous 
round has been excavated, it is important to stake out the first 
row of the second round before the first round is fired. This will 
assure a proper burden on the first row of blastholes in the 
second blast round. 

The burden dimension is a function of the charge diameter. 
For bulk-loaded charges, the charge diameter is equal to the 
blasthole diameter. For tamped cartridges, the charge diame- 
ter will be between the cartridge diameter and the blasthole 
diameter, depending on the degree of tamping. For untamped 
cartridges the charge diameter is equal to the cartridge diameter. 
When blasting with AN-FO or other low density blasting agents 
with densities near 0.85 g/cu cm, in typical rock with a density 
near 2.7 g/cu cm, the normal burden is approximately 25 times 
the charge diameter. When using denser products such as 
slurries or dynamites, with densities near 1 .2 g/cu cm, the 
normal burden is approximately 30 times the charge diameter. 
It should be stressed again that these are first approximations, 
and field testing often results in minor adjustments to these 
values. The burden-to-charge-diameter ratio is seldom less 
than 20 or seldom more than 40, even in extreme cases. For 
instance, when blasting with a low density blasting agent, such 
as AN-FO, in a dense formation such as iron ore, the desired 
burden may be about 20 times the charge diameter. When 
blasting with denser slurries or dynamites in low density forma- 
tions such as some sandstones or marbles, the burden may 
approach 40 times the charge diameter. Table 4 summarizes 
these approximations. 

Table 4. - Approximate B/D ratios for bench blasting 

Ratio 

AN-FO (density— 0.85 g/cu cm): 

Light rock (density — 2.2 g/cu cm) 28 

Average rocl< (density— 2.7 g/cu cm) 25 

Dense rock (density— 3.2 g/cu cm) 23 

Slurry, dynamite (density— 1.2 g/cu cm): 

Ught rock (density— 2.2 g/cu cm) 33 

Average rock (density— 2.7 g/cu cm) 30 

Dense rock (density— 3.2 g/cu cm) 27 

B Burden D Charge diameter 

High-speed photographs of blasts have shown that flexing 
of the burden plays an important role in rock fragmentation. A 
relatively long, slender burden flexes, and thus breaks more 
easily than a short, stiffer burden. Figure 71 shows the differ- 
ence between using a 6-in blasthole and a 12V4-in blasthole in 
a 40-ft bench, with a burden-to-charge-diameter ratio of 30 
and appropriate subdrilling and stemming dimensions. Note 
the inherent stiffness of the burden with the 12y4-in blasthole 
as compared with the 6-in blasthole. Based on this consideration, 
lower burden-to-charge-diameter ratios should be used as a 
first approximation when the blasthole diameter is large in 
comparison to the bench height. Care must be taken that the 
burden ratio is not so small as to create violence. Once the 
burden has been determined, it becomes the basis for calculat- 
ing sutxjrilling, collar distance (stemming), and spacing. 



y 



Figure 71. — Comparison of a 12V4-in-diameter (A) \ 
blasthole (stiff burden) with a 6-in-diameter (B) blasthole 
(flexible burden) in a 40-ft bench. 



pronounced parting at floor level, to which the explosive charge 
can conveniently break, subdrilling may not be required. In 
coal stripping, it is common practice to drill down to the coal 
and then backfill a foot or two before loading explosives, 
resulting in a negative subdrill. In most surface blasting jobs, 
however, it is necessary to do some subdrilling to make sure 
the shot pulls to grade. A good first approximation for subdrilling 
under average conditions is 30 pet of the burden. Where the 
toe breaks very easily, the subdrill can sometimes be reduced 
to 10 to 20 pet of the burden. Even under the most difficult 
conditions, the subdrill should not exceed 50 pet of the burden. 
If the toe cannot be pulled with a subdrill-to-burden ratio of 0.5, 
the fault probably lies in too large a burden. 

Priming the explosive column at the toe level gives maxi- 
mum confinement and normally gives the best breakage. Other 
factors being equal, toe priming usually requires less subdrilling 
than collar priming. 

Too much subdrilling is a waste of drilling and blasting 
expense and may also cause excessive ground vibrations 
owing to the high degree of confinement of the explosive in the 
bottom of blasthole, particulariy when the primer is placed in 
the bottom of the hole. In multiple-bench operations, exces- 
sive subdrilling may cause undue fracturing in the upper por- 
tion of the bench below, creating difficulties in collaring holes 
in the lower bench. Insufficient subdrilling will cause high 
bottom, resulting in increased wear and tear on equipment 
and expensive secondary blasting. Table 5 summarizes the 
recommended subdrilling approximations. 

Table 5. - Approximate J/B ratios for bench blasting 



Open bedding plane at toe 
Easy toe 
Normal toe 
Difficult toe 



B Burden J Subdrilling 



SUBDRILLING 



COLLAR DISTANCE 
(STEMMING) 



Subdrilling is the distance drilled below the floor level to 
assure that the full face of rock Is removed. Where there Is a 



Collar distance is the distance from the top of the explosive 
charge to the collar of the blasthole. This zone is usually filled 



63 



with an inert material called stemming to give some confine- 
ment to the explosive gases and to reduce airblast. Research 
has shown that crushed, sized rock works best as stemming 
but it is common practice to use drill cuttings because of 
economics. Too small a collar distance results in excessive 
violence in the form of airblast and flyrock and may cause 
backbreak. Too large a collar distance creates boulders in the 
upper part of the bench. The selection of a collar distance is 
often a tradeoff between fragmentation and the amount of 
airblast and flyrock that can be tolerated. This is especially 
true where the upper part of the bench contains rock that is 
difficult to break. In this situation the difference between a 
violent shot and one that fails to fragment the upper zone 
properly may be a matter of only a few feet of stemming. Collar 
priming of blastholes normally causes more violence than 
center or toe priming, and requires the use of a longer collar 
distance. 

Field experience has shown that a collar distance equal to 
70 pet of the burden is a good first approximation except where 
collar priming is used. Careful observation of airblast, flyrock, 
and fragmentation will enable the blaster to further refine this 
dimension. Where adequate fragmentation in the collar zone 
cannot be attained while still controlling airblast and flyrock, 
deck charges or satellite holes may be required (fig. 63). 

A deck charge is an explosive charge near the top of the 
blasthole, separated from the main charge by inert stemming. 
If boulders are being created in the collar zone but the operator 
fears that less stemming would cause violence, the main 
charge should be reduced slightly and a deck charge added. 
The deck charge is usually shot on the same delay as the main 
charge or one delay later. Care must be exercised not to place 
the deck charge too near the top of the blasthole, or excessive 
flyrock may result. As an altemative, short satellite holes tjetween 
the main blastholes can be used. These satellite holes are 
usually smaller in diameter than the main blastholes and are 
loaded with a light charge of explosives. 

From the standpoint of public relations, collar distance is a 
very important blast design variable. One violent blast can 
permanently alienate neighbors. In a delicate situation, it may 
be best to start with a collar distance equal to the burden and 
gradually reduce this if conditions permit. Collar distances 
greater than the burden are seldom necessary. 



SPACING 

Spacing is defined as the distance between adjacent 
blastholes, measured perpendicular to the burden. Where the 
rows are blasted one after the other as in figure 68, the spacing 
is measured between holes in a row. However, in figure 69, 
where the blast progresses on an angle to the original free 
face, the spacing is measured at an angle from the original 
free face. 

Spacing is calculated as a function of the burden and also 
depends on the timing between holes. Too close a spacing 
causes crushing and cratering between holes, boulders in the 
burden, and toe problems. Too wide a spacing causes inade- 
quate fracturing between holes, accompanied by humps on 
the face and toe problems between holes (fig. 72). 

When the holes in a row are initiated on the same delay 
period, a spacing equal to twice the burden will usually pull the 
round satisfactorily. Actually, the V-cut round in figure 69 also 
illustrates simultaneous initiation within a row, with the rows 
being the angled lines of holes fired on the same delay. The 
true spacing is twice the true burden even though the holes 
were originally drilled on a square pattern. 



INSUFFICIENT SPACING 




Figure 72.— Effects of insufficient and excessive 
;pacing. 



Field experience has shown that the use of millisecond 
delays between holes in a row results in better fragmentation 
and also reduces the ground vibrations produced by the blast. 
When millisecond delays are used between holes in a row, the 
spacing-to-burden ratio must be reduced to somewhere between 
1 .2 and 1 .8, with 1 .5 being a good first approximation. Various 
delay patterns may be used within the rows, including alter- 
nate delays (fig. 73) and progressive delays (fig. 74). Generally, 
large-diameter blastholes require lower spacing-to-burden ratios 
(usually 1 .2 to 1 .5 with millisecond delays) than small-diameter 
blastholes (usually 1 .5 to 1 .8). Because of the complexities of 
geology, the interaction of delays, differences in explosive and 




n 

O) 

Figure 73. — Staggered blast pattern with alternate 
delays (spacing, S, is 1.4 times the burden, B). 




» I— • 



Figure 74. — Staggered blast pattern with progressive 
delays (spacing, S, is 1.4 times the burden, B). 



64 



rock strengths, and other variables, the proper spacing-to- 
burden ratio must be determined through onsite experimentation, 
using the preceding values as first approximations. 

Except when using controlled blasting techniques such as 
smooth blasting and cushion blasting, which will be described 
later in this chapter, the spacing should never be less than the 
burden. 



HOLE DEPTH 

In any blast design it is important that the burden and the 
blasthole depth (or bench height) be reasonably compatible. 
As a rule of thumb for bench blasting, the hole depth-to-burden 
ratio should be between 1 .5 and 4.0. Hole depths less than 1 .5 
times the burden cause excessive airblast and flyrock and, 
because of the short, thick shape of the burden, give coarse, 
uneven fragmentation. Where operational conditions require 
a ratio of less than 1 .5, the primer should be placed at the toe 
of the bench to assure maximum confinement. Keep in mind 
that placing the primer in the subdrill can cause increased 
ground vibrations. If an operator continually finds use of a hole 
depth-to-burden ratio of less than 1 .5 necessary, consider- 
ation should be given to increasing the bench height orusing a 
smaller drill. 

Hole depths greater than four times the burden are also 
undesirable. The longer a hole is in respect to its diameter the 
more error there will be in its location at toe level, which is the 
most critical portion of the blast. A poorly controlled blast will 
result. Extremely long, slender holes have even been known 
to intersect. 

High benches with short burdens also create hazards, such 
as a small drill having to put in the front row of holes near the 
edge of a high ledge or a small shovel having to dig at the toe of 
a precariously high face. The obvious solution to this problem 
is to use a lower bench height. There is no real advantage to a 
high bench height. Lower benches give more efficient blasting 
results, lower drilling cost and chances for cutoffs, and are 
safer from an equipment operation standpoint. If it is impracti- 
cal to reduce the bench height, larger drilling and rock hand- 
ling equipment should be used, which will effectively reduce 
the blasthole depth-to-burden ratio. 

A major problem with long slender charges is the greater 
potential for cutoffs in the explosive column. Where it is neces- 
sary to use blast designs with large hole depth-to-burden 
ratios, multiple priming should be used as insurance against 
cutoffs. 



DELAYS 

Millisecond delays are used between charges in a blast 
round for three reasons: 

1 . To assure that a proper free face is developed to enable 
the explosive charge to efficiently fragment and displace its 
burden. 

2. To enhance fragmentation between adjacent holes. 

3. To reduce the ground vibrations created by the blast. 

There are numerous possible delay patterns, several of 
which were covered in figures 68, 69, 73, and 74. 

Andrews (1), of du Pont, conducted numerous field investiga- 
tions to determine optimum delay intervals for bench blasting 
and reached the following conclusions. 



ADEQUATE DELAYS 



Figure 75. — The effect of inadequate delays between 



1 . The delay time between holes in a row should be between 
1 and 5 ms per foot of burden. Delay times less than 1 ms per 
foot of burden cause premature shearing between holes, result- 
ing in coarse fragmentation. If an excessive delay time is used 
between holes, rock movement from the first hole prevents the 
adjacent hole from creating additional fractures between the 
two holes. A delay of 3 ms per foot of burden gives good 
results in many kinds of rock. 

2. The delay time between rows should be two to three 
times the delay time between holes in a row. This is longer 
than most previous recommendations. However, in order to 
obtain good fragmentation and control flyrock, a sufficient 
delay is needed so that the burden from previously fired holes 
has enough time to move forward to accommodate broken 
rock from subsequent rows. If the delay between rows is too 
short, movement in the back rows will be upward rather than 
outward (fig. 75). 

3. Where airblast is a problem, the delay between holes in a 
row should be at least 2 ms per foot of spacing. This will 
prevent airblast from one charge from adding to that of subse- 
quent charges as the blast proceeds down the row. 

4. For the purpose of controlling ground vibrations, most 
regulatory authorities consider two charges to be separate 
events if they are separated by a delay of 9 ms or more. 

Following these recommendations should yield good blast- 
ing results. However, when using surface delay systems such 
as detonating cord connectors and sequential timing blasting 
machines, the chances for cutoffs will be increased. To solve 
this problem, in-hole delays should be used in addition to the 
surface delays. For instance, when using surface detonating 
cord connectors, one might use a 100-ms delay in each hole. 
This causes ignition of the in-hole delays well in advance of 
rock movement, thus minimizing cutoffs. With a sequential 
timer, the same effect can be accomplished by avoiding the 
use of electric caps with delays shorter than 75 to 100 ms. 

From the standpoint of simplicity in blast design it is best if all 
the explosive in a blasthole is fired as a single column charge. 
However, it is sometimes necessary, where firing large blastholes 
in populated areas, to use two or more delayed decks within a 
blasthole to reduce ground vibrations. Blast rounds of this type 
can become quite complex, and should be designed under the 
guidance of a competent person. 

All currently used delay detonators employ pyrotechnic delay 
elements. That is, they depend on a burning powder train for 
their delay. Although these delays are reasonably accurate, 



65 



overlaps have been known to occur (9). Therefore, when it is 
essential that one charge fires before an adjacent charge, 
such as in a tight corner of a blast, it is a good idea to skip a 
delay period. Development of blasting caps with electronic 
delays is a good future possibility. 



POWDER FACTOR 

Powder factor, in the opinion of the authors, is not the best 
tool for designing blasts. 

Blast designs should be based on the dimensions discussed 
earlier in this chapter. However, powder factor is a necessary 
calculation for cost accounting purposes. In b'asting opera- 
tions such as coal stripping or construction work where the 
excavated material has little or no inherent value, powder 
factor is usually expressed in terms of pounds of explosive per 
cubic yard of material broken. Powder factors for surface 
blasting can vary from 0.25 to 2.5 Ib/cu yd, with 0.5 to 1 .0 Ib/cu 
yd being most typical. 

Powder factor tor a single blasthole is calculated by the 
following formula: 



P.P. 



L(0.3405d)(D2) 
(B)(S)(H)/(27) 



where P.P. = powder factor, pounds of explosive per cubic 
yard of rock, 
L = length of the explosive charge, feet, 
d = density of the explosive, grams per cubic centi- 
meter, 
D = charge diameter, inches, 
8 = burden dimension, feet, 
S = spacing dimension, feet, 
H = bench height, feet. 



and 



Many explosives companies publish tables that give loading 
densities in pounds per foot of blasthole for different combina- 
tions of d and D. The nomograph in figure 14 also calculates 
the density in pounds per foot of borehole. Powder factor is a 
function of type of explosive, rock density, and geology. Table 
6 gives typical powder factors for surface blasting. 

Higher energy explosives, such as those containing large 
amounts of aluminum, can break more rock per pound than 
lower energy explosives. However, most of the commonly 
used explosive products have fairly similar energy values and 
thus have similar rock breaking capabilities. Soft, light rock 
requires less explosive per yard than hard, dense rock. Large- 
hole patterns require less explosive per yard of rock blasted 
because a larger proportion of stemming is used. Of course, 
larger blastholes frequently result in coarser fragmentation 
because of poorer powder distribution. Massive rock with few 
existing cracks or planes of weakness requires a higher pow- 
der factor than a formation that has numerous, closely spaced 
geologic flaws. Finally, the more free faces a blast has to break 



Table 6. - Typical powder factors for surfac3 blasting 



Degree oi difficulty 
in rock breakage 



Powder factor , 
Ib/cu \ 



Low 

Medium 
High 
Very high 



to, the lower will be the powder factor. For instance a corner 
cut, with two vertical free faces, will require less powder than a 
box cut with only one vertical free face; and a box cut will 
require less powder than a sinking cut, which has only the 
ground surface as a free face. In a sinking cut it is desirable, 
where possible, to open a second free face by using a V-cut 
somewhere near the center of the round. V-cuts are discussed 
in more detail in the "Underground Blasting" section of this 
chapter. 

When blasting materials that have an inherent value per ton, 
such as limestone or metallic ores, powder factors are some- 
times expressed as pounds of explosive per ton of rock or tons 
of rock per pound of explosive. 



SECONDARY 
BLASTING 

Some primary blasts, no matter how well designed, will 
leave boulders that are too large to be handled efficiently by 
the loading equipment or large enough to cause plugups in 
crushers or preparation plants. Secondary fragmentation tech- 
niques must be used to break these boulders. 

In the case of boulders too large to be handled, the loader 
operator will set the boulders aside for treatment. Identifying 
material large enough to cause plugups is not always quite so 
apparent. The operator must be instructed to watch for mate- 
rial that is small enough for convenient loading but which is 
large enough to cause a bottleneck later in the processing 
cycle. 

Secondary fragmentation can be accomplished in four ways: 

1 . A heavy ball suspended from a crane may be dropped 
repeatedly on the boulder until the boulder breaks. This is a 
relatively inefficient method, and breaking a large or tough 
(nonbrittle) rock may take a considerable period of time. This 
method is adequate where the number of boulders produced 
is not excessive. 

2. A hole may be drilled into the boulder and a wedging 
device inserted to split the bouider. This is also a slow method 
but may be satisfactory where only a limited amount of second- 
ary fragmentation is necessary. An advantage of this method 
is that it does not create the flyrock associated with explosive 
techniques or, to some degree with drop balls. 

3. Loose explosive may be packed into a crack or depres- 
sion in the bouider, covered with damp earthen material, and 
fired. This type of charge is called a mudcap, plaster, or adobe 
charge. This method is inefficient because of a lack of explo- 
sive confinement, and relatively large amounts of explosive 
are required. The result is considerable noise and flyrock, and 
often, an inadequately broken boulder. The system is hazard- 
ous because the primed charge, lying on the surface, is prone 
to accidental initiation by external impacts from falling rocks or 
equipment. External charges should be used to break boul- 
ders only where drilling a hole is impractical, and when used, 
extreme caution concerning noise, flyrock, and accidental 
initiation through impact must be exercised. If it is found neces- 
sary to shoot a multiple mudcap blast, long delays or cap and 
fuse are not recommended. 

4. The most efficient method of secondary fragmentation is 
through the use of small (1- to 3-in) boreholes loaded with 
explosives. The borehole is normally collared at the most 
convenient location such as a crack or a depression in the 



66 



rock, and is directed toward the center of mass of the rock. The 
hole is drilled two-thirds to three-fourths of the way through the 
rock. Because the powder charge is surrounded by free faces, 
less explosive is required to break a given amount of rock than 
in primary blasting. One-quarter pound per cubic yard will 
usually do the job. Careful location of the charge is more 
important than its precise size. When in doubt it is best to 
estimate on the low side and underload the boulder. With 
larger boulders it is best to drill several holes to distribute the 
explosive charge, rather than placing the entire charge in a 
single hole. All secondary blastholes should be stemmed. As a 
cautionary note, secondary blasts are usually more violent 
than primary blasts. 



Any type of initiation system may be used to initiate a 
secondary blast. For connecting large numbers of boulders, 
where noise is not a problem, detonating cord is often used. 
The "Detonating Cord Initiation" section in chapter 2 describes 
precautions to be taken against cord cutoffs. Electric blasting 
is also frequently used. 

Although secondary blasting employs relatively small cnarges, 
its potential hazards must not be underestimated. Flyrock is 
often more severe and more difficult to predict than with pri- 
mary blasting. Secondary blasts require at least as much care 
in guarding as do primary blasts. Secondary blasting can truly 
be called an art, with experience being an important key to 
success. 



UNDERGROUND BLASTING 



Underground blast rounds can be divided into two basic 
categories — (1) heading, drift, or tunnel rounds, in which the 
only free face is the surface from which the holes are drilled, 
and (2) bench or stope rounds in which there is one or more 
free faces in addition to the face on which the blastholes are 
drilled. Blasts falling under the second category are designed 
in the same way as surface blast rounds. This discussion will 
cover blasts falling under the first category, only one initial free 
face. 

OPENING CUTS 

The initial and most critical part of a heading round is the 
opening cut. The essential function of this cut is to provide 
additional free faces to which the rock can be broken. The du 
Pont Blaster's Handbook (4) discusses opening cuts. Although 
there are many specific types of opening cuts, and the terminol- 
ogy can be quite confusing, all opening cuts fall into one of two 
classifications; angled cuts, and parallel hole cuts (fig.76). 

An angled cut, which may be referred to as a V-cut, draw 
cut, slab cut, or pyramid cut, breaks out a wedge of rock to 
create an opening to which the remaining holes can displace 
their burdens. Angled cuts are difficult to drill accurately. The 
bottoms of each pair of cut holes should be as close as 
possible. If they cross, the depth of round pulled will be less 
than designed. If bottoms are more than a foot or so apart, the 
round may not pull to its proper depth. The angle between the 
cut holes should be 60° or more, to minimize bootlegging. 
Some mines that drill a standard angled cut supply their drill- 
ers with a template to assure proper spacing and angles of the 
angled holes. The selection of the specific type of angled cut is 
a function of the rock, the type of drilling equipment, the 
philosophy of mine management, and the individual driller. A 
considerable amount of trial and error is usually involved in 
determining the best angled cut for a specific mine. In small 
openings it is often impossible to position the drill properly to 
drill an angled cut. In this case a parallel hole cut must be used. 

Parallel hole cuts, which may also be called Michigan cuts, 
Cornish cuts, shatter cuts, burn cuts, or Coromant cuts, are 
basically a series of closely spaced holes, some loaded and 
some not loaded (fig. 77) which, when fired, pulverize and 
eject a cylinder of rock to create an opening to which the 
burdens on the remaining holes can be broken. Because they 
require higher powder factors and more drilling per volume of 
rock blasted, the use of parallel hole cuts is usually restricted 
to narrow headings, where there is not enough room to drill an 
angled cut. 



ANGLED CUTS 



iii=i!aiiiiiai]Mj= '\ pm\ mi\fs\\ 



mm. 




PARALLEL HOLE CUTS 
Large-hole 



mmmiim/sjiii^ \mifjmiii=nikj//i 



Figure 76. — Types of opening cuts. 



Parallel hole cuts involve more drilling than angled cuts 
because the closely spaced holes break relatively small vol- 
umes of rock. However, they are relatively easy to drill because 
the holes are parallel. Like angled cuts, accurately drilled 
parallel hole cuts are essential if the blast round is to pull 
properly. Some drill jumbos have automatic controls to assure 
that holes are drilled parallel. Units of this type are a good 
investment for mines that routinely drill parallel hole cuts. A 
template may also be used in drilling a parallel hole cut (fig. 
78). 

The selection of the type of parallel hole cut depends on the 
rock, the type of drilling equipment, the philosophy of mine 
management, and the individual driller. As with angled cuts. 



67 





• 






• O • 




• 


o 


o 


• 


o 


• 




O O 




o 


o 


• 




• 






• 
• 




• 


o 


o 




• 






• 




• 




000 



• 

KEY 


• 


• 







• 


• 










• Loaded holes Unloaded holes 







Figure 77.— Six designs for parallel hole cuts. 

trial and error is usually involved in determining the best paral- 
lel hole cut for a specific mine. 

For all types of opening cuts it is important that the cut pulls 
to its planned depth, because the remainder of the round will 



not pull more deeply than the cut. In blasting with burn cuts, 
care must be exercised not to overload the burn holes, as this 
may cause the cut to "freeze" or not pull properly. Proper 
loading of the cut depends on the design of the cut and the 
type of rock being blasted, and often must be determined by 
trial and error. 

Some research has been done involving burn cuts with one 
or more large central holes (8), and a few mines have adopted 
this practice. The advantage of the large central hole is that it 
gives a dependable void to which succeeding holes can break, 
which is not always obtained with standard burn cuts. This 
assures a more dependable and deeper pull of the blast 
round. The disadvantages of the large central hole are the 
requirement for an extra piece of equipment to drill the large 
hole and the extra time involved. Sometimes a compromise is 
used where intemiediate-sized holes, such as 4- or 5-in diameter, 
are drilled using the same equipment used to drill the standard 
blastholes. 

In some soft materials, particularly coal, the blasted cut is 
replaced by a sawed kerf, usually at floor level (fig. 79). In 
addition to giving the material a dependable void to which to 
break, the sawed cut assures that the floor of the opening will 
be smooth. 




Figure 78.— Drill template for parallel hole cut. (Courtesy Ou Pont co.) 




Side view 



liiV|ii^ii)siii=r/isi/'-/«=-|ii = i|iH ///»'" " i;i^/;)sj/;^///^///^//^//=///= 



Front view 



lll=IIIS^II^III=^IISIII=-lf,- 



-iii=-iiisiitsiii^iii^tiis tiisili-s-iii=_ 



rilSIII:slllzlllZJil^l^,l-/ll 



V-CUT ROUND 
Top view 



SLABBING ROUND 
Top view 






Figure 81. — Angled cut blast rounds. 



Figure 79. — Blast round for soft material using a 
sawed kerf. 



BLASTING 
ROUNDS 

Once the opening cut has established the necessary free 
face, the remainder of the blastholes must be positioned so 
that they successively break their burdens into the void space. 
It is important to visualize the progression of the blast round so 
that each hole, at its time of initiation, has a proper free face 
parallel or nearly parallel to it. Figure 80 gives the typical 
nomenclature for blastholes in a heading round. 

The holes fired immediately after the cut holes are called the 
relievers. The burdens on these holes must be carefully planned. 

If the burdens are too small the charges will not pull their 
share of the round. If the burdens are too large the round may 
freeze owing to insufficient space into which the rock can 
expand. After several relievers have been fired, the opening is 
usually large enough to permit the design of the remainder of 



''•4 


• 4 


• 4 


• 4 


4« 


4« 


4« 


4« 


•3 




• 


•2 

• 1 


2» 
O !• 






3« 


• 3 




• 


O 




• 1 






3» 


•3 




• 


• 2 


2« 






3« 


•5 


•5 


•5 


•5 


5« 


5» 


5« 


5* 



Empty holes 


3 Rib holes 


1 Looded burn holes 


4 Bock holes 


2 Helper? or relievers 


5 Lifters 



the blast in accordance with the principles discussed under 
the "Surface Blasting" section. In large heading rounds, the 
burden and spacing ratios are usually slightly less than those 
for surface blasts. In small headings, where space is limited, 
the burden and spacing ratios will be still smaller. This is 
another area where trial and error plays a part in blast design. 

The last holes to be fired in an underground round are the 
back holes at the top, the rib holes at the sides, and the lifters 
at the bottom of the heading. Unless a controlled blasting 
technique is used (discussed later in this chapter) the spacing 
between these perimeter holes is about 20 to 25 blasthole 
diameters. Figure 81 Shows two typical angled cut blast rounds. 
After the initial wedge of rock is extracted by the cut, the angles 
of the subsequent blastholes are progressively reduced until 
the perimeter holes are parallel to the heading or looking 
slightly outward. In designing burden and spacing dimensions 
for angled cut blast rounds, the location of the bottom of the 
hole is considered rather than the collar. 

hlgure 82 shows two typical parallel hole cut blast rounds. It 
can be seen that these rounds are much simpler to drill than 
angled cut rounds. Once the central opening has been 
established, the round resembles a bench round turned on its 



REGULAR 
Top view 



LARGE-HOLE 



Top view 

! 



^ii^iiiUii 



Front view 

= lll5|l|Sll(=ll|Slf|SWS/ll=|/| = 



isi//;S|(;si;;/3:(|i/ = i 




IllSinslll S./llSJII=:i/l-3ll S// S-lll=^ 



Figure 80. — Nonrtenclature for Diastholes in a heading round. 



Figure 82.— Parallel hole cut blast rounds. 




Figure 83.— Fragmentation and shape of muclcpile 
as a function of type of cut. 

side. Figure 83 shows a comparison of typical muckpiles 
obtained from V-cut and burn-cut blast rounds. Burn cuts give 
more uniform fragmentation and a more compact muckpile 
than V-cuts, where the muckpile is more spread out and 
variable in fragmentation. Powder factors and the amount of 
drilling required are higher for burn cuts. 



^•10 


• 9 


• 8 


• 7 




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loT 


• 9 


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• 6 


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9* 


• 8 


• 7 


• 5 





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5» 


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• 9 


• 8 


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6» 


8« 


9« 


•10 


• 9 


• 8 


• 7 




7» 


8* 


9« 


I0« 



O Unloaded hole 



•9 Loaded hole with delay 



Figure 85. — Typical burn cut blast round delay pattern. 



FRONT VIEW 






^ •? •S •S •0 




3» 5« 7« 



•8 •6 •4 •2 I ^- ^- ^- „-^ ,„ 



DELAYS 

Two series of delays are available for underground blasting; 
millisecond delays, which are the same as those used in 
surface blasting, and slow, or tunnel delays. The choice of 
delay depends on the size of the heading being blasted and on 
the fragmentation and type of muckpile desired. Slow delays 
give coarser fragmentation and usually give a more compact 
muckpile whereas millisecond delays give finer fragmentation 
and a more spread out muckpile (fig. 84). In small headings 
where space is limited, particularly when using parallel hole 




KEY 
•''Loaded hole with delay period 

Figure 86. — Typical V-cut blast round delay pattern. 



^^uais^ii^j^ue^ 



SLOW DELAY 




^^^^f^^^^ 



MILLISECOND DELAY 




Figure 84.— Fragmentation and shape of muckpile 
as a function of delay. 



BACK HOLES FIRED LAST 




Figure 87.— Shape of muckpile as a function of order 
of firing. 



70 



cut rounds, slow delays are necessary to assure that the rock 
from each blasthole has time to be ejected before the next hole 
fires. Where a compromise between the results of millisecond 
delays and slow delays is desired, some operators use milli- 
second delays and skip delay periods. 

In an underground blast round it is essential that the delay 
pattern be designed so that each hole, at its time of firing, has a 
good free face to which it can displace its burden. Figure 85 
shows a typical delay pattern for a burn cut blast round in a 
heading in hard rock. Figure 86 shows a delay pattern for a 
V-cut blast round. 

The shape of the muckpile is affected by the order in which 
the delays are fired (fig. 87). If the blast is designed so that the 
back holes at the roof are fired last, a cascading effect is 



obtained, resulting in a compact muckpile. If the lifters are fired 
last, the muckpile will be displaced away from the face. 



POWDER 
FACTOR 

As with surface blasting, powder factors for underground 
blasting vary depending on several factors. Powder factors for 
underground blasting may vary from 1 .5 to 12 Ib/cu yd. Soft, 
light rock, headings with large cross sections, large blastholes, 
and angle cut rounds all tend to give lower powder factors than 
hard, dense rock, small headings, small blastholes, and paral- 
lel hole cuts. 



UNDERGROUND COAL MINE BLASTING 



Underground coal mine blasting is different from most rock 
blasting in two important respects. Operations take place in a 
potentially explosive atmosphere containing methane and coal 
dust, and the coal is much easier to break than rock. The 
loading and firing methods, as well as the explosive type, must 
be permissible, as specified by the Mine Safety and Health 
Administration (MSHA). In addition, underground coal mine 
blasting is closely regulated by State regulatory agencies. 
This discussion is intended to point out some of the main 
differences between coal blasting and rock blasting and should 
not be considered as a guide to regulatory compliance. Per- 
sons involved in underground coal mine blasting need to 
become thoroughly familiar with the MSHA regulations deal- 
ing with permissible blasting, which are identified in Appendix 
A, and those of the State in which they blast. Hercules (6) has 
published a shotfirer's guide for underground coal mine blasting. 

Black powder or other nonpermissible explosives, including 
detonating cord, may not be stored or used in underground 
coal mines. Unconfined shots, that is, those not contained by 
boreholes, may not be fired although a permissible, external 
charge is currently under development. In most States the 
coal must be undercut (fig. 79) before blasting. The boreholes 
should not be deeper than the cut to assure that the coal is not 
fired off the solid. The minimum depth of cut should be SVa ft. 

Charge weights should not exceed 3 lb per borehole. Bore- 
holes should have a minimum 1 8-in burden in all directions. If 
this specification cannot be met, the charge weight should be 



reduced to prevent underburdened shots. Blast rounds should 
be limited to 20 holes. All holes should be bottom primed with 
the cap at the back of the hole, although this is not always 
required by regulation. Aluminum-cased detonators should 
not be used and leg wires should not be more than 16 ft long, 
or of equivalent resistance. Permissible blasting machines are 
designed to provide sufficient energy to a circuit using the 
rated number of electric blasting caps with 1 6-ft iron leg wires. 
Should these machines be used with copper wire detonators, 
their apparent capacity is increased. Zero-delay detonators 
should not be used in a circuit with millisecond-delay detonators. 
Permissible explosives must remain in the original cartridge 
wrapper throughout storage and use, without admixture with 
other substances. Cartridges must be loaded in a continuous 
train, in contact with each other, and should not be deliberately 
crushed, deformed, or rolled. Permissible explosives must 
conform with their original specifications, within limits of toler- 
ance prescribed by MSHA. The cartridge must be of a diame- 
ter which has been approved. All blastholes must be stemmed 
with incombustible material. Holes deeper than 4 ft should 
contain at least 24 in of stemming and holes less than 4 ft deep 
should be stemmed for at least half their length. Water stem- 
ming bags, when used, should be at least 15 in long and 
should have a diameter within V* in of the borehole diameter. 
Shots must be fired with a permissible blasting unit of ade- 
quate capacity. 



CONTROLLED BLASTING TECHNIQUES 



The term controlled blasting is used to describe several 
techniques for improving the competence of the rock at the 
perimeter of an excavation. Du Pont, among other companies, 
has published an excellent pamphlet describing and giving 
general specifications for the four primary methods of con- 
trolled blasting (5). Much of this discussion is adapted from 
that publication. The recommended dimensions have been 
determined through years of on-the-job testing and evaluation. 
These recommended dimensions are given as ranges of values. 
The best value for a given blasting job is a function of the 
geology, specifically the number and severity of planes of 
weakness in the rock, and the quality of rock surface that is 



required. Normal blasting activities propagate cracks into the 
excavation walls. These cracks reduce the stability of the 
opening. The purpose of controlled blasting is to reduce this 
perimeter cracking and thus increase the stability of the opening. 
Figure 88 shows a stable slope produced by controlled blasting. 



LINE 
DRILLING 

Line drilling involves the drilling of a row of closely spaced 
holes along the final excavation line. It is not really a blasting 



71 




Figure 88. — Stable slope produced by controlled blasting. (Courtesy Austin Powder co.) 



technique since the line-drilled holes are not loaded with 
explosive. The line-drilled holes provide a plane of weakness 
to which the final row of blastholes can break and also reflect a 
portion of the blast's stress wave. Line drilling is used mostly in 
small blasting jobs and involves small holes in the range of 2- 
to 3-in diameter. Line drilling holes are spaced (center to 
center) two to four diameters apart. The maximum practical 
depth to which line drilling can be done is governed by how 
accurately the alignment of the holes can be held at depth, and 
js seldom more than 30 ft. 

To further protect the final perimeter, the blastholes adja- 
cent to the line drill are often more closely spaced and are 
loaded more lightly than the rest of the blast, using deck 
charges and detonating cord downlines if necessary. Best 
results are obtained in a homogeneous rock with little jointing 
or bedding, or when the holes are aligned with a major joint 
plane. 

The use of line drilling is limited to jobs where even a light 
load of explosives in the perimeter holes would cause unaccept- 
able damage. The results of line drilling are unpredictable, the 
cost of drilling is high, and the results are heavily dependent on 
the accuracy of drilling. Table 7 gives average specifications 
for line drilling. 



Table 7. - Average specifications for line drilling 



Hole diameter, In 



2.00.. 
3.00. 



Spacing, ft 

0.33-0.67 

.50-1.00 



PRESPLITTING 

Presplitting, sometimes called preshearing, is similar to line 
drilling except that the holes are drilled farther apart and a very 
light load of explosive is used in the holes. Presplit holes are 
fired before any of the main blastholes adjacent to the presplit 
are fired. Although the specific theory of presplitting is in 
dispute, the light explosive charges propagate a sheared zone, 
preferably a single crack, between the holes, as shown in 
figure 89. In badly fractured rock, unloaded guide holes may 
be drilled between the loaded holes. The light powder load 
may be obtained by using specially designed slender cartridges, 
partial or whole cartridges taped to a detonating cord downline, 
explosive cut from a continuous reel, or even heavy grain 
detonating cord. A heavier charge of tamped cartridges is 
used in the bottom few feet of hole. Figure 90 shows three 



72 




Figure 89. — Crack generated by a presplit blast. (Courtesy Austin Powder co.) 



73 




-Heavier toe loads 

Figure 90.— Three typical blasthole loads for presplitting. 



types of blasthole loads used for presplitting. Many operators 
now use %- or Va-in by 2-ft cartridges connected with couplers. 

It is desirable to completely stem around and between the 
cartridges in the borehole. It is also desirable, although not 
essential, to fire all the presplit holes on the same delay period. 
The maximum depth for a single presplit is limited by the 
accuracy of the drillholes, and is usually about 50 ft. A devia- 
tion of greater than 6 in from the desired plane of shear will 
give inferior results. One should avoid presplitting far ahead of 
the production blast. It is preferable to presplit a shorter sec- 
tion and dig that section out so that the quality of the presplit 
can be checked. If the presplit is unsatisfactory, adjustments 
can be made in subsequent blasts. 

Some operators prefer to fire the presplit with the main blast 
by firing the presplit holes on the first delay period. Although 
presplitting is usually thought of as a surface blasting technique, 
it is occasionally used underground. The increased hole spac- 
ing reduces drilling costs as compared with line drilling. Table 
8 gives average specifications for presplitting. 



Table 8. - Average specifications for presplitting 



SMOOTH BLASTING 

Smooth blasting, also called contour blasting, perimeter 
blasting, or sculpture blasting, is the most widely used method 
of controlling overbreak in underground openings such as 
drifts and stopes. It is similar to presplitting in that it involves a 
row of holes at the perimeter of the excavation that is more 
lightly loaded and more closely spaced than the other holes in 
the blast round. The light powder load is usually accomplished 
by "string loading" slender cartridges. Unlike presplitting, the 
smooth blast holes are fired after the main blast. This is usually 
done by loading and connecting the entire round and firing the 
perimeter holes one delay later than the last hole in the main 
round. As a first approximation, the burden on the perimeter 
holes should be approximately 1 .5 times the spacing, as shown 
in figure 91 . Table 9 gives average specifications for smooth 
blasting. 

As a compromise between standard blasting and smooth 
blasting some operators slightly reduce the spacing of their 
perimeter holes, as compared with standard design, and string 
load regular cartridges of explosive. It is recommended proce- 
dure to seal the explosive column with a tamping plug, clay 
dummy, or other object to prevent the string-loaded charges 
from being extracted from the hole by charges on earlier 
delays. 



B>S 




•6 



•7 



• 8 



•2 O 2« 
O O 



• 5 



•7 



•3 



• 6 



3« 



6« 



4« 



59 



1% 



6« 



!• 



8« 



KEY 



O Unloaded hole 



•7 Loaded hole with 
delay period 



Figure 91 .—Typical smooth blasting pattern (burden, 
B, is larger than spacing, S). 



Hole 
diameter, 


Spacing, 

ft 


Explosive 

charge, 

lb/ft 


Table 9. - 


Average specifications for smooth blasting 


in 


Hole 

diameter, 

in 


Spacing, 


Burden, 
ft 


Explosive 


1.50-1.75 
2.00-2.50 


1,00-1.50 
1.50-2.00 
1.50-3.00 
2.00-4.00 


0.08-0.25 
,08- ,25 
,13- ,50 
,25- ,75 


charge, 
lb/ft 


3.00-3.50 
4.00 


1,50-1.75 
2,00 


2,00 
2,50 


3.00 
3.50 


0.12-0,25 
,12- ,25 



74 



Smooth blasting reduces overbreak and reduces the need 
for ground support. This usually outweighs the cost of the 
additional perimeter holes. 



CUSHION BLASTING 

Cushion blasting is surface blasting's equivalent to smooth 
blasting. Like other controlled blasting techniques, it involves 
a row of closely spaced, lightly loaded holes at the perimeter of 
the excavation. Holes up to 6y2 in in diameter have been used 
in cushion blasting. Drilling accuracy with this size borehole 
permits depths of up to 90 ft for cushion blasting. After the 
explosive has been loaded, stemming is usually placed in the 
void space around the charges. The holes are fired after the 
main excavation is removed. A minimum delay between the 
holes is desirable. The same loading techniques that apply to 
presplitting are used with cushion blasting, except that the 
latter often involves larger holes. The burden on the cushion 
holes should always be larger than the spacing between holes. 



The larger holes associated with cushion blasting result in 
larger spacings as compared with presplitting, thus reducing 
drilling costs. Better results can be obtained in unconsolidated 
formations than with presplitting, and the larger holes permit 
better alignment at depth. Table 10 gives average specifica- 
tions for cushion blasting. 



Table 10. - Average specifications for cushion blasting 



Hole 


Spacing, 


Burden, 


Explosive 


diameter, 


ft 


ft 


charge, 


in 






lb/ft 


2.00-2.50 


3.00 


4.00 


0.08-0.25 


3.00-3.50 


4.00 


5.00 


.13- .50 


4.00-4.50 


5.00 


6.00 


.25- .75 


5.00-5.50 


6.00 


7.00 


.75-1.00 


6.00-6.50 


7.00 


9.00 


1.00-1.50 



REFERENCES 



1. Andrews, A. B. Design of Blasts. Emphasis on Blasting. Ensign 
Bickford Co. (Simsbury, CN), Spring 1980, pp. 1, 4. 

2. Ash, R. L. The Mechanics of Rock Breakage, Parts I, II, III, and 
IV. Pit and Quarry, v. 56, No. 2, August 1963, pp. 98-112; No. 3, 
September 1963, pp. 1 18-123; No. 4, October 1963, pp. 126-131 ; No. 
5, November 1963, pp. 109-1 11,114-118. 

3. Dick, R. A., and J. J. Olson. Choosing the Proper Borehole Size 
for Bench Blasting. Min. Eng., v. 24, No. 3, March 1972, pp. 41-45. 

4. E. I. du Pont de Nemours & Co., Inc. (Wilmington, DE). Blaster's 
Handbook. 16th ed., 1978, 494 pp. 

5. Four Major Methods of Controlled Blasting. 1 964, 1 6 pp. 



6. Hercules, Inc. (Wilmington, DE). Shotfirer's Guide. 1978, 12 pp. 

7. Pugleise, J. M. Designing Blast Patterns Using Empirical Formulas. 
BuMines IC 8550, 1972, 33 pp. 

8. Schmidt, R. L., R. J. Morrell, D. H. Irby, and R. A. Dick. Applica- 
tion of Large-Hole Burn Cut In Room-and-Pillar Mining. BuMines Rl 
7994,1975,25 pp. 

9. Winzer, S. R. The Firing Times of MS Delay Blasting Caps and 
Their Effect on Blasting Performance. Prepared for National Science 
Foundation (NSF APR 77-05171). Martin Marietta Laboratories 
(Baltimore, MD), June 1978, 36 pp.; available for consultation at 
Bureau of Mines Twin Cities Research Center, Minneapolis, MN. 



75 



Chapter 5.— ENVIRONMENTAL EFFECTS OF BLASTING 



There are four environmental effects of blasting. 

1. Flyrock 

2. Ground vibrations 

3. Airblast 

4. Dust and gases 

Flyrock is a potential cause of death, serious injury, and 
property damage. Ground vibrations and airblast are potential 
causes of property damage and human annoyance, but are 
very unlikely to cause personal injury. Flyrock, ground vibrations, 
and airblast all represent wasted explosive energy. Excessive 
amounts of these undesirable side effects are caused by 
improper blast design or lack of attention to geology. When 
excessive side effects occur, part of the explosive energy that 
was intended to give the proper amount of rock fragmentation 
and displacement is lost to the surrounding rock and atmosphere. 
Serious dust or gas problems are seldom caused by blasting. 
A larger than normal amount of dust may be caused by a 
violent shot. Noxious gases, normally oxides of nitrogen or 
carbon monoxide, are the result of an inefficient explosive 
reaction. Because of its sporadic nature, blasting is not a 
significant source of air pollution. 

When blasting in the vicinity of structures (fig. 92) such as 
homes, hospitals, schools, and churches, a preblast survey, 
documenting the condition of the structures, is often beneficial. 



A preblast survey has a twofold purpose. First, it increases 
communications between the community and the mine operator. 
It has long been recognized that good public relations are the 
operator's best means of reducing blasting complaints. A preblast 
survey helps the operator to maintain good community relations. 
Many companies have been conducting preblasting surveys 
for years and have found them to be an excellent investment. 

The second purpose of a preblast survey is to provide a 
baseline record of the condition of a structure against which 
the effects of blasting can be assessed. When combined with 
a postblast survey, this will help assure equitable resolution of 
blast damage claims. Office of Surface Mining (OSM) regula- 
tions require that a preblast survey be conducted, at the home- 
owners request, on all homes within 0.5 mi of blasting at 
surface coal mines. 

Good blast recordkeeping is essential to any successful 
blasting operation. A blasting record is useful in troubleshoot- 
ing the cause of undesirable blasting results such as flyrock, 
airblast, ground vibrations, and poor fragmentation. The blast- 
ing record may also provide excellent evidence in litigation on 
blast damage or nuisance. Figure 93 gives an example of a 
blasting record. Depending on the blasting situation, some of 
the information contained in figure 93 may not be required. On 
the reverse side of the blasting record a sketch of the blast 
pattern, including delays, and a sketch of a typical loaded hole 
should be drawn. 




Figure 92.— Mining near a residential structure. 



76 



BLASTING RECORD 

Date:_ 

Company - 



Location of blast :_ 

Tine of blast: 

Date of blast: 



Name of blaster: License No: 



Direction: Distance: f eet frcan blast to nearest dwelling, 

school, church, conmercial, or institutional building. 

Weather data: Temperature : Wind direction 

and speed: Cloud cover: 

Type of material blasted: 



No. of holes : ^Burden : ^Spacing : ^Depth : ^Diam. : 

Type of explosive used: 

Maximum weight of explosive detonated within any 9-ms period: lb. 

Maximum number of holes detonated within any 9-ms period: 

Total weight of explosives, including primers, this blast: lb. 

Method of firing and type of circuit: 

Type and length of stanming: 

Were mats or other protection used? 



Type of delay detonator used: Delay periods used: 

Seismic data: T , V , L , dB 

Location of seismograph: Distance from blast: ^ft. 

Name of person taking seismograph reading:^ 

Name of person and firm analyzing the seismograph record: 



Signed : Blaster 

Figure 93. — Example of a blasting record. 



77 



FLYROCK 



Flyrock, primarily associated with surface mining, is the 
most hazardous effect of blasting. It is a leading cause of 
onsite fatalities and equipment damage from blasting. Occa- 
sionally flyrock will leave the mine site and cause serious 
injury and damage to persons and property beyond the mine 
limits. Flyrock distances can range from zero, for a well-controlled 
coal strip-mine blast, to nearly a mile for a poorly confined, 
large, hard-rock mine blast. The term flyrock can be defined as 
an undesirable throw of material. Muckpile displacements on 
the order of 100 ft are often desirable for certain types of 
loading equipment such as front-end loaders. Even larger 
displacements may be desirable for explosive casting of waste 
material. 



CAUSES AND 
ALLEVIATION 



consultation with the drill operator and through past experi- 
ence in the area being blasted. An abnormal lack of resistance 
to drill penetration usually indicates a mud seam, a zone of 
incompetent rock, or even a void. The driller should note the 
depth and the severity of this zone of weakness on the drill log. 
Any explosive loaded in this zone will follow the line of least 
resistance and "blow out," causing flyrock (fig. 59). Placing a 
few feet of stemming, rather than explosive, in this area will 
reduce the likelihood of flyrock (fig. 62). Void zones such as 
mine openings or solution cavities cause violent explosions 
when packed with explosives. It is always a good idea to 
measure the buildup of -the column as explosive loading 
proceeds. If buildup is abnormally slow, the zone should be 
stemmed and the powder column continued above it. Measur- 
ing the column buildup will also assure that adequate room is 
left for stemming above the charge. 



Excessive flyrock is most often caused by an improperly 
designed or improperly loaded blast (5).'' A burden dimension 
less than 25 times the charge diameter often gives a powder 
factor too high for the rock being blasted. The excess explo- 
sive energy results in long flyrock distances. On the other 
hand, an excessively large burden may cause violence in the 
collar zone, especially where an inadequate amount or an 
ineffective type of stemming is used. This situation is com- 
pounded when top priming is used, as opposed to center or 
toe priming. 

To prevent or correct flyrock problems, the blaster should 
make sure that the burden is proper and that enough collar 
distance is used. One-fourth-inch-size material makes better 
stemming than fines, particularly where there is water in the 
boreholes. In some cases it may be necessary to lengthen the 
stemming zone above the main charge and use a small deck 
charge to reduce flyrock and still assure that the caprock is 
broken. Top initiation is a particularly poor practice where 
flyrock is a problem. In multiple row shots, longer delays 
between later rows, on the order of 10 ms per foot of burden, 
may reduce flyrock. Precautions should be taken against cut- 
offs when using delays of this length. 

Zones of weakness and voids are often causes of flyrock. 
These potential problems can sometimes be foreseen through 



PROTECTIVE 
MEASURES 

Despite careful planning and good blast design, flyrock may 
occasionally occur and must always be protected against. 
Some margin for error must always be maintained. Abnor- 
mally long flyrock distances should be measured and recorded 
for future reference. The size of the guarded perimeter should 
take these cases into account. An adequate number of guards 
must be posted at safe distances. Any persons within this 
perimeter must have safe cover and must be adequately 
warned. Remember that warning signs, prearranged blasting 
times, or warning sirens, in themselves, are seldom adequate 
for blast guarding. It is particularly good if the blaster has a 
commanding field of view of the blast area so he or she can 
abort the shot at the last minute if necessary. 

OSM surtace coal mine regulations prohibit throwing flyrock 
beyond the guarded zone, more than one-half the distance to 
the nearest dwelling or occupied structure, and beyond the 
operator's property line. State and local flyrock regulations 
may also exist. In small, close-in construction blasts, special 
protective mats may be used to contain flyrock. However, this 
is impractical in mine blasts or other large blasts. 



GROUND VIBRATIONS 



All blasts create ground vibrations. When an explosive is 
detonated in a borehole it creates a shock wave that crushes 
the material around the borehole and creates many of the 
initial cracks needed for fragmentation. As this wave travels 
outward, it becomes a seismic, or vibration wave. As the wave 
passes a given piece of ground it causes that ground to 
vibrate. The situation is similar to the circular ripples produced 
on the surface of a pool of calm water when it is struck by a 
rock (6). Ground vibrations are measured with seismographs 
(12) (fig. 94). They are measured in terms of amplitude (size of 
the vibrations) and frequency (number of times the ground 

^ Italicized numbers in parentheses refer to items in the list of refer- 
ences at the end of this chapter. 



moves back and forth in a given time period). In blasting, 
amplitude is usually measured in terms of velocity (inches per 
second) and frequency is measured in hertz, or cycles per 
second. Excessively high ground-vibration levels can damage 
structures. Even moderate to low levels of ground vibration 
can be irritating to neighbors and can cause legal claims of 
damage and/or nuisance. One of the best protections against 
claims is good public relations (1). While striving to minimize 
ground vibrations, the blaster or the company should inform 
local residents of the need for and the importance of the 
blasting, and the relative harmlessness of properly controlled 
blasting vibrations when compared to the day-to-day stresses 
to which a structure is subjected. Prompt and sincere response 
to complaints is important. 



78 




Figure 94. — Seismograph for measuring ground vibrations from blasting. 



CAUSES 

Excessive ground vibrations are caused either by putting 
too much explosive energy into the ground or by not properly 
designing the shot. Part of the energy that is not used in 
fragmenting and displacing the rock will go into ground vibrations. 
The vibration level at a specific location is primarily deter- 
mined by the maximum weight of explosives that is used in any 
single delay period in the blast and the distance of that location 
from the blast (9). 

The delays in a blast break it up into a series of smaller, very 
closely spaced individual blasts. The longer the intervals are 



between delays, the better the separation will be between the 
individual blasts. Most predictive schemes and regulatory agen- 
cies use a guide of 8 or 9 ms as the minimum delay that can be 
used between charges if they are to be considered as sepa- 
rate charges for vibrations purposes. However, there is noth- 
ing magical about the 8- or 9-ms interval. For small, close-in 
blasts a smaller delay may give adequate separation. 

With large blasts at large distances from structures, longer 
delays are required to obtain true separation of vibrations 
because the vibration from each individual charge lasts for a 
longer period of time. In general, vibration amplitudes at struc- 
tures sitting on the formation of rock being blasted will be 



79 



greater than at structures sitting on other formations. However, 
they may be higher in frequency, which reduces the response 
of structures and the likelihood of damage. 

In addition to charge weight per delay, distance, and delay 
interval, two factors may affect the level of ground vibrations at 
a given location. The first is overconfinement. A charge with a 
properly designed burden will produce less vibration per pound 
of explosive than a charge with too much burden (fig. 95). An 
excessive amount of subdrilling, which results in an extremely 
heavy confinement of the explosive charge, will also cause 
higher levels of ground vibration, particularly if the primer is 
placed in the subdrilling. In multiple row blasts, there is a 
tendency for the later rows to become overconfined (fig. 75). 
To avoid this, it is often advisable to use longer delay periods 
between these later rows to give better relief. In some types of 
ground these longer delays may increase the chance of cutoffs, 
so some tradeoffs must be made. Second, if delays proceed in 
sequence down a row, the vibrations in the direction that the 
sequence is proceeding will be highest (fig. 96) because of a 
snowballing effect. 

Recent studies C73j have shown that millisecond delays in 
commercial detonators are less accurate than was previously 



2 3 4 



Figure 96. — Effect of delay sequence on particle velocity. 



believed. This may result in extremely close timing between 
adjacent delay periods or, very rarely, an overlap. Where it is 
critical that one hole detonates before an adjacent hole to 
provide relief, it may be a good idea to skip a delay period 
between the two holes. 

Most underground mines shoot relatively small blasts and 
do not have vibration problems. However, where vibrations 
are a problem, the discussions in this chapter apply to under- 
ground blasting as well as surface blasting. 



NORMAL VIBRATIONS 



Jll=J'/'.**VJc=i*^A 



Normal : 
burden 




Normal 
subdril ling 



EXCESSIVE VIBRATIONS 



^-AJIfca','! 




-Excessive 
subdril ling 



Figure 95. — Effects of confinement on vibration levels. 



PRESCRIBED VIBRATION LEVELS AND 
MEASUREMENT TECHNIQUES 

Two vibration limits are important; the level above which 
damage is likely to occur and the level above which neighbors 
are likely to complain. There is no precise level at which 
damage begins to occur. The damage level depends on the 
type, condition, and age of the structure, the type of ground on 
which the structure is built, and the frequency of the vibration, 
in hertz. Research completed by the Bureau of Mines in the 
late 1 970's {9) recommends that for very close-in construction 
blasting, where the frequency is above 40 Hz, vibration levels 
be kept below 2 in/sec to minimize damage. However, all mine 
and quarry blast vibrations, and those from large construction 
jobs, have frequencies below 40 Hz. For these blasts it is 
recommended that the vibration level be kept below 0.75 
in/sec for homes of modern, drywall construction and below 
0.50 in/sec for older homes with plaster-on-lath walls. These 
values could change as more research is done. 

People tend to complain about vibrations far below the 
damage level. The threshold of complaint for an individual 
depends on health, fear of damage (often greater when the 
owner occupies the home), attitude toward the mining operation, 
diplomacy of the mine operator, how often and when blasts 
are fired, and the duration of the vibrations. The tolerance level 
could be below 0.1 in/sec where the local attitude is hostile 
toward mining, where the operator's public relations stance is 
poor, or where numerous older persons own their homes. On 
the other hand where the majority of people depend on the 
mine for their livelihood, and where the mine does a good job 
of public relations, levels above 0.50 in/sec might be tolerated. 
By using careful blast design and good public relations it is 
usually possible for an operator to live in harmony with neigh- 
bors without resorting to expensive technology. 

Several options are available for measuring ground vibra- 
tions (M). Many operators prefer to hire consultants to run 
their monitoring programs. Either peak reading seismographs 
or seismographs that record the entire vibration event on a 
paper record may be used. Peak reading instruments are 



80 



cheaper, easier to use, and are adequate for assuring regula- 
tory compliance in most cases. However, seismographs that 
record the entire time history are more useful for understand- 
ing and troubleshooting ground vibration problems. Instru- 
ments that measure three mutually perpendicular components 
(radial, transverse, vertical) are most common, and most regula- 
tions specify this type of measurement. Vector sum instru- 
ments will always give a higher reading (usually 10 to 25 pet 
higher) than the highest single component of a three-component 
instrument. Because vector sum instruments always give a 
higher reading, they should be satisfactory for regulatory com- 
pliance even where the regulation specifies three components. 

Some seismographs require an operator to be present while 
others operate remotely, usually for a period of a month between 
battery changes. Operator-attended instruments are cheaper 
but require the expense of the operator. They can be moved 
from place to place to gather specific data on specific blasts. 
Remotely installed instruments are useful in that they record 
each blast without sending an operator out each time. These 
instruments should be installed in places that are protected 
from weather and tampering. When recording remotely, it is 
easier to detect tampering with seismographs that record the 
entire time history than with peak readjng instruments. 

When accelerations larger than 0^3 g are expected, the 
seismograph should be secured to the ground surface. Many 
instruments are equipped with stakes for this purpose. Epoxy 
or bolting may be used on hard surfaces. Where possible, 
when the expected acceleration level is high, the gage should 
be buried in the ground. 

Seismograph records provide excellent evidence in case of 
later complaints or lawsuits on damage or nuisance from 
blasting. A complete blast record, as shown in figure 93, 
describing the layout, loading, initiation, and other pertinent 
aspects of the blast is also essential. 



SCALED DISTANCE 
EQUATION 

Where vibrations are not a serious problem, regulations will 
often permit the blaster to use the scaled distance equation 
rather than measuring vibrations with a seismograph. The 
scaled distance equation is as follows: 

S.D. = D/W''' 

where S.D. is the scaled distance, D is the distance from the 
blast to the structure of concern, in feet, and Wis the maximum 
charge weight of explosives, in pounds, per delay of 9 ms or 
more. The scaled distance permitted depends on the allow- 
able vibration level. For instance. Bulletin 656 (7) says that a 
scaled distance of 50 or greater will protect against vibrations 
greater than 2 in/sec. Therefore, at a distance of 500 ft, 1 00 lb 
of explosive could be fired; at 1 ,000 ft, 400 lb; at 1 ,500 ft, 900 
lb, etc. The original OSM regulations (2-3) specified a scaled 
distance of 60 or greater to protect against 1 in/sec, giving 
distance-weight combinations of 600 ft and 1 00 lb; 1 ,200 ft and 
400 lb, 1 ,800 ft and 900 lb, etc. This regulation is currently 
being revised. 



The scaled distance approach works well when the mine is 
an adequate distance from structures, vibrations are not a 
problem, and the operator wants to save the expense of 
measuring vibrations. At close distances, however, the scaled 
distance becomes quite restrictive in terms of allowable charge 
weights per delay and monitoring is often a more economical 
option. 



RED UCING G ROUND 
VIBRATIONS 

A properly designed blast using the principles described in 
chapter 4 will give lower vibrations per pound of explosive than 
a poorly designed blast. Proper blast design includes using a 
spacing-to-burden ratio equal to or greater than 1 .0, using 
proper delay patterns, and using a proper powder factor. 
Blasthole locations should be carefully laid out and drilling 
should be controlled as closely as possible. Bench marks 
should be established for use in setting out hole locations for 
the next blast before the current blast is made to avoid possi- 
ble errors due to backbreak (4). 

The following techniques can be used to reduce ground 
vibrations: 

1 . Reduce the charge weight of explosives per delay. This 
is most easily done by reducing the number of blastholes fired 
on each delay. If there are not enough delay periods available, 
this can be alleviated by using a sequential timer blasting 
machine or a combination of surface and in-hole nonelectric 
delays. The manufacturer should be consulted for advice when 
using the sequential timer or complex delay systems. If the 
blast already employs only one blasthole per delay, smaller 
diameter blastholes, a lower bench height, or several delayed 
decks in each blasthole can be used. Delays are often required 
when presplitting. 

2. Overly confined charges such as those having too much 
burden or too much subdrilling should be avoided. The primer 
should not be placed in the subdrilling. Where it appears that a 
later row of blastholes will have inadequate relief, a delay 
period should be skipped between rows. 

3. The length of delay between charges can be increased. 
This is especially helpful when firing large charge weights per 
delay at large blast-to-structure distances. However, this will 
increase the duration of the blast and may cause more adverse 
reactions from neighbors. 

4. If delays in a row are arranged in sequence, the lowest 
delay should be placed in the hole nearest the structure of 
concern. In other words, the shot should be propagated in a 
direction away from the structure. 

5. The public's perception of ground vibrations can be reduced 
by blasting during periods of high local activity such as the 
noon hour or shortly after school has been dismissed. Blasting 
during typically quiet periods should be avoided, if possible. 



AIRBLAST 



Airblast is a transient impulse that travels through the 
atmosphere. Much of the airblast produced by blasting has a 



frequency below 20 Hz and cannot be heard effectively by the 
human ear. However, all airblast, both audible and inaudible. 




Figure 97.— Blasting seismograph with microphone for measuring airblast. 



can cause a structure to vibrate in much the same way as 
ground vibrations (8, 10). Airblast is measured with special 
gages, pressure transducers, or wide-response microphones 
(1 1). These instruments are often an integral part of blasting 
seismographs (fig. 97). As with ground vibrations, both ampli- 
tude and frequency are measured. Amplitude is usually mea- 
sured in decibels, sometimes in pounds per square inch, and 
frequency is measured in hertz. Research has shown that 
airblast from a typical blast has less potential than ground 
vibrations to cause damage to structures. It is, however, fre- 
quently the cause of complaints. When a person senses vibra- 
tions from a blast, or experiences house rattling, it is usually 
impossible to tell whether ground vibrations or airblast is being 
sensed. A discussion of airblast should be part of any mine 
public relations program. 



CAUSES 

Airblast is caused by one of three mechanisms (6) as shown 
in figure 98. The first cause is energy released from uncon- 
fined explosives such as uncovered detonating cord trunklines 



Stemming release 




Figure 98.— Causes of airblast. 



82 



or mudcaps used for secondary blasting. The second cause is 
the release of explosive energy from inadequately confined 
borehole charges. Some examples are inadequate stemming, 
inadequate burden, or mud seams. The third cause is move- 
ment of the burden and the ground surface. Most blasts are 
designed to displace the burden. When the face moves out, it 
acts as a piston to form an air compression wave (airblast). For 
this reason, locations in front of the free face receive higher 
airblast levels than those behind the free face. 



PRESCRIBED AIRBLAST LEVELS AND 
MEASUREMENT TECHNIQUES 

Siskind (8) has studied the problem of damage from airblast. 
Table 1 1 shows the airblast levels prescribed for preventing 
damage to structures. 

As indicated in the table, different instruments have different 
lower frequency limits. Because much of the airblast is con- 
tained in these lower frequency levels, some of the instru- 
ments measure more of the airblast than others. That is the 
reason for the different maximum levels in the table. It is 
necessary to meet only one of these values, depending on the 
specifications of the instrument used. 

Because airblast is a major cause of blasting complaints, 
merely meeting the levels given in the table is sometimes not 
sufficient. Airblast levels should be kept as low as possible by 
using the techniques described later in this section. This will 
go a long way toward reducing complaints and conflicts with 
neighbors. 

Any instrument with a frequency range listed in table 1 1 can 
be used to measure airblast. Many operators prefer to hire 
consultants to monitor airblast. Most of the discussion under 
ground vibration measurement techniques also applies to airblast 
measurement. Both peak reading instruments and those that 
record the entire airblast time history are available. The peak 
reading devices are satisfactory for regulatory compliance but 
those that record the entire airblast time history are much 
better for troubleshooting purposes. A single airblast reading 
is taken at a given location. The gage should be 3 to 5 ft above 
the ground and should be at least 5 ft to one side of any 
structure to prevent distortion to the record due to airblast 
reflections. 

Airblast can be measured by an operator-attended instru- 
ment or by a remotely installed instrument. Operator-attended 
instruments are cheaper but require the expense of the operator. 
They are more flexible in that data can be recorded at different 
locations for different blasts. Remotely installed instruments 
are useful in that they record each blast fired without requiring 
an operator each time. One disadvantage of remote monitor- 
ing is that a high reading can be induced by a loud noise near 
the instrument. For this reason, instruments that record the 
entire airblast event are recommended for remote monitoring, 
so that a nonblasting event can be identified by its noncharac- 
teristic wave trace. 

It is recommended that all airblast monitors be equipped 
with wind screens to cut down the background noise level and 
protect the microphone. Remotely installed instruments should 
be protected from the weather. 

Table 11.- Maximum recommended airblast levels 

Frequency range of instrumentation Maximum level, dB 

0.1 to 200 Hz, flat response 134 peak. 

2 to 200 Hz, flat response 133 peak. 

6 to 200 Hz, flat response 129 peak. 

C-weighted, slow response 105 C. 



Airblast recordings provide good evidence in case of com- 
plaints or lawsuits. Airblast readings taken in conjunction with 
ground vibration readings are especially helpful in determining 
which of the two are the primary cause of complaints. 



REDUCING 
AIRBLAST 

Properly executed blasts, where surface explosives are 
adequately covered and borehole charges are adequately 
confined, are not likely to produce harmful levels of airblast. 
Close attention must be paid to geology to prevent the occa- 
sional "one that gets away from you." 

The following techniques can be used to reduce airblast. 

1 . Unconfined explosives should not be used. Where sur- 
face detonating cord is used it should be buried. Cords with 
lighter core loads require less depth of burial. 

2. Sufficient burden and stemming on the blastholes are 
essential. Where the length of stemming is marginal, coarse 
stemming material will give better charge confinement than 
fines, particularly where there is water in the stemming zone. 
One-fourth-inch material makes excellent stemming. A longer 
stemming dimension should be used where part of the burden 
at the crest has been robbed from the front row of holes. The 
front row of holes usually creates more airblast than subse- 
quent rows. 

3. Geologic conditions that cause blowouts should be com- 
pensated for. These include mud seams, voids, or open bed- 
ding (should be stemmed through) and solution cavities or 
other openings (a check of column rise will avoid overloading). 

4. Holes must be drilled accurately to maintain the designed 
burden. This is especially important with inclined holes. 

5. If there is a high free face in the direction of nearby 
built-up areas, the face should be reorientated, if possible, or 
reduced in height. 

6. Collar priming should be avoided where airblast Is a 
problem. (Actually, collar priming is seldom desirable.) 

7. Early morning, late afternoon, or night firing, when tem- 
perature inversions are most likely, should be avoided. Blast- 
ing when a significant wind is blowing toward nearby built-up 
areas will increase airblast. 

8. Use of longer delays between rows than between holes 
in a row will promote forward rather than upward movement of 
the burden. Five milliseconds per foot of burden between rows 
is a good rule of thumb, but this should be increased in later 
rows for shots with many rows. 

9. Excessively long delays that may cause a hole to become 
unburdened before it fires should be avoided. 

Public reaction to airblast can be reduced by blasting during 
periods of high activity such as the noon hour or shortly after 
school has been dismissed. Blasting during quiet periods 
should be avoided. 



DUST AND GASES 



Every blast generates some amount of dust and gases. The 
amounts of dust generated by blasting do not present a seri- 
ous problem. Other phases of the mining operation such as 
loading, hauling, crushing, and processing produce considera- 
bly more dust than blasting. Even though a violent blast may 
produce more than the normal amount of dust, blasting is a 
relatively infrequent operation and, as a result, the total amount 
of dust produced in a day is insignificant when compared to 
other sources. Well controlled blasts create little or no dust. 
Because dust in the muckpile can be a problem to mine 
personnel, it is common practice to thoroughly wet the muckpile 
before and during mucking operations. In underground opera- 
tions an appropriate amount of time is allowed for the dust to 
settle or to be expelled from the area by the ventilation system 
before miners enter the blast area. 

The most common toxic gases produced by blasting are 
carbon monoxide and oxides of nitrogen. While these gases 



are considered toxic at levels of 50 ppm and 5 ppm respectively, 
blast fumes are quickly diluted to below these levels by the 
ventilation systems in underground mines and by natural air 
movement in surface mines. In underground operations, it is 
important to allow time for toxic gases to be expelled by the 
ventilation system before miners enter the area. In surface 
mining, it is a good idea to wait for a short period of time before 
entering the immediate blast area, particularly if orange-brown 
fumes (oxides of nitrogen) are present. It is extremely rare for 
significant concentrations of toxic gases to leave the mine 
property. If large amounts of orange-brown fumes are consis- 
tently present after blasts, the source of the problem should be 
determined and corrected. The primary causes of excessive 
nitrogen oxides are poor blasting agent mixtures, degradation 
of blasting agents during storage, use of non-water-resistant 
products in wet blastholes, and inefficient detonation of the 
blasting agent due to loss of confinement. 



REFERENCES 



1 . Bauer, A., and J. W. Sanders. Good Blasting Techniques and 
Public Relations. Min. Cong. J., v. 54, No. 11, November 1968, pp. 
81-85. 

2. Dick, R. A. A Review of the Federal Surface Coal Mine Blasting 
Regulations. Proc. 5th Conf. on Explosives and Blasting Technique, 
St. Louis. MO, Feb. 7-9, 1979. Society of Explosives Engineers, 
Montville, OH. pp. 1-7. 

3. Dick, R. A., and D. E. Siskind. Ground Vibration Technology 
Pertaining to OSM Regulations. Proc. Symp. on Surface Coal Mining 
and Reclamation Coal Conf. & Expo., Louisville, KY, Oct. 23-25, 
1979. McGraw-Hill, New York, pp. 13-18. 

4. E. I. du Pont de Nemours & Co., Inc. (Wilmington, DE). Blaster's 
Handbook. 16th ed., 1978, 494 pp. 

5. Lundborg, N., P. A. Persson, A. Ladegaard-Pederson, and R. 
Holmberg. Keeping the Lid on Flyrock From Open Pit Blasting. Eng. 
and Min. J, v. 176, No. 5, May 1975, pp. 95-100. 

6. Miller, P. Blasting Vibration and Alrblast. Atlas Powder Co. (Dallas, 
TX). 16 pp. 

7. Nicholls, H. R., C. F. Johnson, and W. I. Duvall. Blasting Vibra- 
tions and Their Effects on Structures. BuMines B 656, 1971, 105 pp. 



8. Siskind, D. E., V. J. Stachura, M. S. Stagg, and J. W. Kopp. 
Structure Response and Damage Produced by Alrblast From Surface 
Mining. BuMines Rl 8485, 1980, 111 pp. 

9. Siskind, D. E. , M. S. Stagg, J. W. Kopp, and C. H. Dowding. 
Structure Response and Damage Produced by Ground Vibration 
From Surface Mine Blasting. BuMines Rl 8507, 1980, 74 pp. 

10. Siskind, D. E., and C. R. Summers. Blast Noise Standards and 
Instrumentation. BuMines TPR 78, May 1974, 18 pp. 

1 1 . Stachura, V. J., D. E. Siskind, and A. J. Engler. Airblast Instru- 
mentation and Measurement Techniques for Surface Mine Blasting. 
BuMines Rl 8508, 1981, 53 pp. 

12. Stagg, M. S., and A. J. Engler. Measurement of Blast-Induced 
Ground Vibrations and Seismograph Calibration. BuMines Rl 8506, 
1980,62 pp. 

1 3. Winzer, S. R. The Firing Times of MS Delay Blasting Caps and 
Their Effect on Blasting Performance. Prepared for National Science 
Foundation (NSF APR 77-05171). Martin Marietta Laboratories 
(Baltimore, MD), June 1978, 36 pp.; available for consultation at 
Bureau of Mines Twin Cities Research Center, Minneapolis, MN. 



85 



Chapter 6.— BLASTING SAFETY 



The following is a discussion of good, safe blasting procedures, 
moving chronologically from initial explosive storage through 
postshot safety measures. In addition to these procedures, 
the blaster must familiarize himself or herself with all the safety 
regulations which govern his or her operation. These safety 
regulations contain additional advice on safe operating proce- 
dures for all phases of the blasting operation. The safety 
procedures discussed here are not meant to be, nor should be 



considered to be, a substitute for adherance to safety regulations. 
Of course, all general workplace safety recommendations 
also apply to blasting activities. 

The Institute of Makers of Explosives (IME) has published 
an excellent series of safety publications (5-13) ^ The National 
Fire Protection Association (NFPA) has published recommen- 
dations on the storage and handling of ammonium nitrate and 
blasting agents (14-16). 



EXPLOSIVES STORAGE 



The Bureau of Alcohol, Tobacco and Firearms (BATF) regu- 
lates explosive importation, manufacture, distribution and 
storage, including proper recordkeeping to protect the public 
from misuse. Safe storage of explosives in the mining industry, 
including BATF regulations, is enforced by the Mine Safety 
and Health Administration (MSHA). In all other industries, safe 
explosive storage is regulated by BATF and the Occupational 
Safety and Health Administration (OSHA). In addition, most 
States, and many county and local government agencies, 
enforce their own explosive safety regulations. 

Magazines for explosive storage must conform to specifica- 
tions laid down by BATF and MSHA or OSHA. IME Pamphlet 
No. 1 (13) gives recommended standards for magazine 
construction. Magazines must be separated from each other, 
surrounding buildings, and rights-of-way according to the Ameri- 
can Table of Distances [IME Pamphlet No. 2 (5)]. Separation 
distance requirements between ammonium nitrate and blast- 
ing agent storage facilities are less than for high explosives. 
However, the distance requirements for separation of blasting 
agents and ammonium nitrate from occupied structures and 
rights-of-way are the same as those for high explosives. Deto- 
nators may not be stored with other explosive materials. High 
explosives must be stored in a type 1 (BATF) or type 2 magazine. 
Blasting agents may be stored in a type 1 magazine with high 
explosives. When explosives and blasting agents are stored 
together, all of the material in the magazine is considered to be 
high explosives for separation distance purposes. Blasting 
agents may be stored in any approved magazine. 



Except when explosives are being deposited or withdrawn, 
magazines must be kept locked. Only authorized personnel 
should deposit or withdraw explosives. The number of author- 
ized persons should be kept to a minimum for both safety and 
security purposes. In this way accountability problems can be 
minimized. Explosive stocks should be piled neatly (fig. 99) to 
facilitate safe handling, and the oldest explosives should be 
used first to assure freshness. This is important for all explo- 
sive materials but especially for AN-FO, to prevent fuel segre- 
gation or evaporation. Segregation and evaporation of fuel 
from AN-FO is a particular problem in bulk storage (fig. 100). 

Prolonged storage should be avoided. Good housekeeping 
standards should be maintained both inside and outside the 
magazine. To minimize the fire hazard, vegetation outside the 
magazine, except live trees over 1 ft high, should be cleared 
for a distance of at least 25 ft and rubbish should be cleared for 
at least 50 ft. Smoking or flames are not permitted in or within 
50 ft of an outdoor storage magazine. Magazines should be 
clearly marked. The IME recommends a sign stating 
"Explosives — Keep Off" in 3-in-high letters with a y2-in brush 
stroke. It is advisable that the explosives sign be placed so that 
a bullet passing through the sign will not strike the magazine. 

Primed explosives must never be stored in magazines. 
Misfired explosives should be disposed of immediately or 
stored in a separate magazine while awaiting disposal 
assistance. Assistance in disposing of deteriorated or unwanted 
explosives will be provided by the explosives distributor upon 
request. 



TRANSPORTATION FROM MAGAZINE TO JOBSITE 



if the route from the magazine to the jobsite leaves company 
property, the transporter is subject to all State and local trans- 
portation regulations regarding vehicle specifications, placarding, 
and other operational procedures. 

Explosive transportation should be done only in an approved 
vehicle in good repair and especially outfitted for the job. The 
practice of using the most conveniently available vehicle for 
explosive transportation should be avoided. The interior of the 
explosives compartment must be constructed of nonsparking 
material. If detonators are to be hauled on the same vehicle as 
explosives, they must be properly separated. MSHA regula- 
tions require a minimum separation by 4-in hardwood or the 
equivalent. Detonators should be protected from electrical 
contact. Adequate fire fighting equipment should be kept on 



the vehicle at all times. Small fires that are clearly isolated from 
the explosive cargo should be fought. However, if fire reaches 
the explosive cargo, the vehicle should be abandoned and 
guarded at a safe distance because it may detonate. 

The operator of the explosives vehicle should be well trained 
in both driving and explosives handling. Before moving out 
with the explosives load, the driver should make sure that the 
explosives cannot fall from the vehicle as frictional impact will 
readily initiate explosives. Explosives transport by rail and 
track equipment is particularly susceptible to the frictional 
impact hazard. 

^ Italicized numbers in parentheses refer to items in the list of references at the 
end of this chapter. 



J 



tlEO DIAMOND 



HIGH eXFUMtVCfrOANCCKOVS 



tlED DIAMOND) 



<#> 

HIGH cxmui^ f'f'^^'???!?. . 

^tO 'DIAMOND 





Figure 99.— Proper stacking of explosives. (Courtesy 



Co.) 



At the jobsite, the explosives should be stored in a safe 
location, away from traffic if possible. The blast area should be 
delineated with cones or cordoned off, and unauthorized per- 
sons should not be pemnitted within this area. Where appropriate, 



the explosives should be stored In an approved day magazine. 
Explosives should not be stored where they can be hit by 
falling rock or working equipment. Explosives should be under 
constant surveillance whenever they are not in a magazine. 



PRECAUTIONS BEFORE LOADING 



Before any loading activities are started, the blast area must 
be clearly marked with flags, cones, or other readily identifi- 
able markers. All unnecessary equipment must be removed 
from this area. All persons not essential to the powder loading 
operation should leave. Observers should be under the con- 
trol of a responsible person who will assure that they do not 
create a hazard by wandering about the area. Any electrical 
power that might create a hazard should be disconnected. 
Where electric blasting is being used and the presence of 



extraneous electricity is suspected, appropriate checks should 
be made with a blasters' multimeter (1) or a continuous ground 
current monitor should be utilized. Where extraneous electric- 
ity problems persist, a nonelectric initiation system should be 
used. Two-way radios in the near vicinity should be turned off 
when electric blasting is being used. IME Pamphlet No. 20 
(10) gives safe transmitter distances as a function of the type 
and power of the transmitter. 



87 




Figure 100.— AN-FO bulk storage facility. (Courtesy Atlas Powder Co.) 



PRIMER PREPARATION 



It is a cardinal rule that primers be made up at the working 
face or as close to it as possible. The detonators and primer 
cartridges or cast primers should be brought in as separate 
components. The preparation of primers at a remote location 
and their transportation to the jobsite presents an undue haz- 
ard on the transportation route and should be permitted only 
where required by extenuating circumstances. In large tunnel 
projects, use of an outside primer makeup facility is often 
considered safer than making the primers at the face. All 
unused primers should be dismantled before removing them 
from the jobsite. Assembled primers containing detonators 
should never be stored. 

A nonsparking tool should be used to punch the hole in the 
cartridge for cap placement. To assure control, the number of 
persons making up primers should be as few as practical. 
Electric hazards should be checked for if electric caps are 
being used. It is extremely important that the cap be fully 
imbedded into the cartridge and attached in such a way that it 
will not be dislodged when tension is put on the wires or tubes. 
A hard cartridge should not be rolled for softening. This will 
destroy the integrity of the cartridge and the cap may not stay 
fully imbedded. A good nonsparking powder punch should 
make an adequate hole in any cartridge without rolling it. The 
dangers of the cap falling out of the cartridge are twofold: (1 ) 
The cap may be struck during loading or tamping operations 
and cause a premature detonation, or (2) the cap may fail to 
initiate the primer when it is activated. When using electric 
caps with small-diameter explosive cartridges, the cartridge 



should be punched at the end for cap insertion and the leg 
wires should be fastened to the cartridge by a half hitch to 
remove the possibility of tension on the cap (fig. 49). 

The structure of larger cartridges may require punching the 
cap hole in the side. With cast primers, the cap is passed 
through the channel and into the cap well (fig.50). The leg 
wires may be taped to the cast primer for extra security. Primer 
preparation for other types of blasting caps, such as Nonel,^ 
Primadet, and Hercudet, is similar to that for electric blasting 
caps. However, because propagation through the tubing of 
some of these products may be hampered by sharp bends, 
tap'ing the tubing to the cartridge is recommended rather than 
half hitching. The manufacturer should be consulted for 
recommendations. 

Where detonating cord is connected directly to the primer 
cartridge, it should be secured with a tight knot, supplemented 
by half hitches. With a cast primer, detonating cord is passed 
through the channel and a knot is tied at the end of the cord to 
keep the primer from slipping off. Subsequent primers can be 
slid down the detonating cord. When using cap and fuse, a 
diagonal hole is made through the cartridge. The cap and fuse 
are passed through this hole and into a second hole made for 
cap emplacement. Sometimes the cap is placed into a single, 
diagonally placed side hole and the fuse is tied to the cartridge 
with string. With fuse that will withstand a 180° bend, end 
priming, similar to that used with electric blasting caps, maybe 
used. Cast primers are not normally used with cap and fuse. 



BOREHOLE LOADING 



Before loading begins, the area should be doublechecked 
for unnecessary personnel and equipment. If electric caps are 
being used, possible electrical hazards should be double- 
checked. If an electrical storm approaches at any time when 
explosives are present, the area must be vacated, regardless 
of whether electric detonators are being used. Weather reports, 
lightning detectors, or even static from AM radio receivers may 
serve as warning of approaching electhcal storms. Before any 
detonators or explosives are brought into the blast area, all 
circuits in the immediate vicinity should be deenergized. 

Before loading begins, each borehole should be checked 
for proper depth. This will help prevent excessive column 
buildup, resulting in inadequate stemming and excessive flyrock. 
In most situations, holes that are too deep should be partially 
backfilled. Short holes may require cleaning or redrilling. 

Using a weighted tape, tne column buildup should be cnecked 
frequently during loading. With relatively short, small-diameter 
holes, a tamping pole can be used to check the depth and also 
to check for blockages. If the buildup is less than anticipated, 
this may result in a cavity packed full of explosive which may 
blow out violently when detonated. If the column builds up 
more quickly than expected, frequent checking will prevent 
overloading. Proper stemming length is described in the "Blast 
Design" chapter. As a general rule of thumb, the stemming 
should be 1 4 to 28 borehole diameters. 

When loading small-diameter cartridges, a nonsparking tamp- 
ing pole should be used. Although there are differences of 
opinion, there is a consensus that a cushion stick should not 



be used in small-diameter holes; therefore, the primer should 
be the first cartridge placed into the hole. The base of the cap 
should point toward the collar. The primer cartridge should 
never be slit and should be pushed into place firmly. It should 
never be tamped vigorously. Two or three cartridges may then 
be slit, placed as a column, and tamped firmly. The remaining 
cartridges may be slit and tamped firmly. Excessive tamping 
should never be done. Care should be taken not to damage 
the detonator's leg wires or tubes. 

Cartridges are often loaded in large-diameter blastholes by 
dropping them down the hole. However, the primer cartridge 
and a cartridge or two above the primer should be lowered to 
prevent damage to the primer. Leg wires or tubes from detona- 
tors may also be prone to damage from dropped cartridges. 
"Wet bags" of AN-FO should not be dropped. They depend on 
the cartridge material for water resistance, and dropping them 
may break the package and cause water leakage and subse- 
quent desensitization of the AN-FO. A potential problem in 
bulk loading of large diameter blastholes is overloading. Here 
it is especially important to check the column rise frequently as 
loading progresses (fig. 101). 

When pneumatically loading blastholes with pressure pots 
or venturi loaders, over electric blasting cap leg wires, it is 
essential that the loader be properly grounded to prevent 
buildup of static electricity. This grounding should not be to 



^Reference to specific trade names does not imply endorsement by 
the Bureau of Mines. 




i 



Figure 101— Checking the rise of the AN-FO column with a weighted tape. 



90 



pipes, air lines, rails, or other fixtures that are good conductors 
of stray current. Extraneous electricity is also a potential haz- 
ard with nonelectric detonators. Plastic liners should not be 
used when pneumatically loading small blastholes, as this 
increases the chance for static buildup. This is particularly 
hazardous with electric detonators. A semiconductive loading 
hose with a minimum resistance of 1 ,000 ohms/ft and 10,000 
ohms total resistance, and a maximum total resistance of 



2,000,000 ohms should be used. Such a hose will permit a 
static charge to bleed off but will not allow stray currents to 
enter the borehole. Where extraneous electricity is a problem, 
or where it is illegal to load pneumatically over leg wires, a 
nonelectric initiation system should be used. This does not 
entirely eliminate the hazard, so the safeguards mentioned 
previously should still be followed. 



HOOKING UP THE SHOT 



The size of crew used to hook up the shot should be kept to 
an absolute minimum. A single person should be in charge of 
final checkout to assure that the hookup plan has been prop- 
erly followed and that the blast is ready to fire. 

When blasting electrically, the series circuit is the easiest, 
safest, and surest. If several shots are to be fired together, or if 
there is an excessive number of caps in one shot, a parallel 
series circuit should be used. Make sure that each series has 
the same resistance. A twisted loop is the best connection for 
two relatively light gage wires. Splices for connecting light 
gage wire to heavy gage wires are shown in figure 22. Exces- 
sive wire between holes may be coiled or removed for neat- 
ness and to facilitate visual inspection of the circuit. Make sure 
that bare connections do not touch each other or the ground in 
order to avoid short circuits, current leakage, or picking up of 
extraneous currents. 

After each portion of the circuit has been hooked up, check 
for continuity and proper resistance with a blasting multimeter 
or galvanometer. The circuit should then be shunted until 
ready for the final hookup prior to blasting. It is especially 
important that the lead wire be kept shunted at the shotfirer's 
location until the blast is ready to be fired. 

A blasting machine is recommended for firing all shots. If a 
powerline is used it should be one that is specifically dedicated 
to blasting and is equipped with a safeguard against 
overenergizing the caps and against the resulting arcing. Bat- 
teries should never be used for firing electrical blasting circuits 
because their output is unpredictable and may cause only a 
portion of the round to be fired. Parallel circuits are less desir- 
able because they require high current and cannot be checked 
for shorts or broken wires. If powerline firing or straight parallel 
circuits are necessary, the cap manufacturer should be con- 
sulted for procedures for minimizing problems. 

When firing with detonating cord systems, make sure the 



knots are tight and secure. Tight lines and severe angles 
between lines should be avoided (fig. 32). The cord should not 
be permitted to cross itself. The cord circuit should be laid out 
so that each hole can be initiated by at least two paths from the 
detonator used to initiate the circuit. After the hookup has been 
completed, the circuit should be carefully checked visually by 
the person in charge of the blast. The initiating cap should not 
be connected to the detonating cord until it is time to blast. 

When blasting with fuse, the use of Ignitacord is recom- 
mended for multiple hole blasts. A principal cause of fuse 
accidents is trying to light too many fuses at one time. Second- 
ary causes are wet or deteriorated fuse and insufficient or 
improper lighting equipment. When using Ignitacord, all fuses 
should be the same length. The path of the Ignitacord will 
determine the delay sequence. The Ignitacord should not 
cross itself, because crosslighting is a possibility. At least two 
persons must be present when lighting fuses. If fuses are 
being individually lit, no person shall light more than 1 5 fuses. 
MSHA regulations specify burning times for fuses, depending 
on the number of fuses a person lights. The burning speed of 
fuse should be tested frequently. All fuse burns nominally at 
about 40 sec/ft. All fuses must be burning inside the hole 
before the first hole detonates. 

Accident rates show that fuse blasting is inherently more 
hazardous than other initiation methods. Many of these inci- 
dents occur with highly experienced miners. It is recommended 
that, wherever practical, fuse blasting be replaced by an alter- 
native initiation system. When using the more recently devel- 
oped initiation systems such as Hercudet, Detaline, and Nonel, 
the blaster should seek advice on the proper hookup proce- 
dures from the manufacturer or distributor. Certain aspects of 
these systems are still evolving and recommended proce- 
dures change from time to time. 



SHOT FIRING 



More people are injured and killed during the shot firing 
operation than any other phase of blasting. This is usually due 
to inadequate guarding, improper signaling, or some other 
unsafe practice that permits a person to be too close to the 
blast when it is detonated. It is essential that the blaster take 
positive steps to assure that no one, including the blaster and 
the crew, is in the area of potential flyrock at the time of 
detonation. 

The blaster should allow adequate time immediately before 
blasting to inspect the blast area for any last minute problems. 
He or she should have a fail-safe system to assure that the 
blast is not inadvertently fired. This can be done by safeguard- 



ing the key or handle to the blasting machine or switch. While 
proceeding from the loaded shot toward the shotfiring location, 
the blaster should make sure that all connections between the 
blasting circuit and the firing mechanism are intact. 

The blaster must make sure that there are enough guards to 
seal off the area and protect persons from inadvertently pro- 
ceeding into the blast area. It is common procedure to block 
access to the blast zone 5 to 10 min before the blast. The 
guards should proceed outward from the blast area, clearing 
all personnel from the area as they proceed. They should take 
up guard positions beyond the range of flyrock, concussion, 
and toxic gases. Once the area has been sealed off, the 



91 



guards must permit no one to pass unless they first inform the 
shotfirer and receive assurance from the shotfirer that he or 
she will postpone the blast. 

A warning siren with an audible range of about 0.5 mi should 
be sounded before the blast. However, signs or audible warn- 
ings alone are not dependable for keeping people out of the 
blast area. These types of warning may not be understood by 
all persons in the area and they do not clearly delineate the 
hazardous area. Many underground mines have check-in and 
checkout procedures that are used to assure that no one will 
stray into the blast area. These systems reduce the number of 
guards required. The guards must be told if more than one 
blast is to be fired. Even after all blasts have been fired, it is 
important that the guards receive an audible or visual all-clear 
signal before allowing persons to pass. If the guard is in doubt, 
he or she should keep the area secure until the doubt is 
removed. 

The shotfirer should choose a safe firing location with ade- 
quate distance and/or cover (fig. 102) for protection from 
flyrock, concussion, and toxic gases. Ideally he or she should 
have two-way visual or audible contact with the guards. On a 
surface blast the shotfiring location should command a good 
view of the area surrounding the blast. Just before the shotfiring 



mechanism is prepared for activation the blaster should alert 
the guards to seal off the area and should receive a positive 
response from each guard. Immediately before firing the shot 
guards are again alerted and if their response is positive, the 
shot is fired. If the shot fails to fire, security must be maintained 
while the blaster attempts to correct the problem. Once secu- 
rity is removed, the entire guarding procedure should be repeated 
before the shot is fired. 

In some situations, particularly underground, contact between 
the shotfirer and the guards may be impractical. In this case, 
the guards must clear and secure the area and maintain 
security until all shots are fired or until they are relieved of the 
responsibility by the blaster. This may mean guarding the area 
for an extended period of time. 

Obviously some situations will exist which will not fit the 
preceding discussion. The principles, however, will remain the 
same — (1 ) the blast area must be cleared and guarded and (2) 
security must be maintained until it is certain that the blasting 
activities in the area have ceased for the time in question. 

Blasting at night at surface mines is especially hazardous 
because of the lack of visibility and should be done only in an 
emergency. 





I3I.ASTING 
SHELTER 




Figure 102. — Blasting shelter. (Courtesy Hercules Inc.j 



92 



POSTSHOT SAFETY 



At least 1 5 sec should be allowed for all f lyrock to drop. Even 
after all flyrock has subsided, the hazards of toxic gases and 
loose rock in the blast area exist. The area should not be 
reentered until the toxic gases have been dispersed. The time 
required for th'd may range from a minute for surface blasting 
to an hour or more for a poorly ventilated underground opening. 
In case of a known or suspected misfire, a waiting period of at 
least 30 min with cap-and-fuse blasting or at least 15 min with 
electric initiation systems must be observed. If explosives are 
suspected to be burning in a blasthole, a 1 -hr minimum waiting 
period must be observed. The practice of blasting between 
shifts is recommended because it avoids or minimizes guard- 
ing problems and allows gases to clear before reentry. 



The first person reentering the blast area should inspect the 
area for loose rock that poses a hazard to personnel. The area 
should be dangered off until any loose rock has been barred 
down or othenwise taken care of. The blast area should be 
checked for misfires. Loose explosives or detonating cord in 
the muckpile often indicate a misfire. Leg wires, detonating 
cord, or tubes extending from a borehole may indicate a 
misfire. Another indicator is an area of the blast that has not 
broken or pulled properly or an unusual shape of the muckpile. 
In many cases this takes the form of an unusually long bootleg. 
Because a misfire is not always obvious, a trained eye is often 
required to detect one. Other persons must not be permitted 
into the blast area until it is certain that no hazards exist. 



DISPOSING OF MISFIRES 



A good method of misfire disposal is to remove the 
undetonated charge by water flushing or air pressure. Horizon- 
tal or shallow holes are most amenable to this technique. It is 
important to visually inspect the hole using a light source to 
assure that all of the charge has been removed. 

Where removal of the misfired charge is too difficult, an 
alternative is to detonate the charge. If leg wires, tubes, or 
detonating cord are protruding from the holes, and they are 
intact, they may be reconnected and fired. If this cannot be 
done, the stemming may be removed, a new primer inserted at 
the top of the powder column, and the hole retired. Caution 
must be exercised in retiring misfired holes from which much 
of the burden has been removed. Excessive flyrock is likely to 
result and the area must be guarded accordingly. If neither of 



these alternatives are feasible, the charge will have to be dug 
out. First, the hole should be flooded with water to desensitize 
any non-water-resistant explosive present. Next, the rock sur- 
rounding the misfire is dug out carefully, with an observer 
present to guide the excavator. Extreme discretion must be 
exercised in this operation. 

The practice of drilling and shooting a hole adjacent to the 
misfire has been used, but can be extremely hazardous. Peo- 
ple have been killed using this technique when the new hole 
intersected the misfired hole and detonated it. All of the pre- 
viously described techniques are preferable to drilling an adja- 
cent hole. MSHA metal-nonmetal regulations prohibit drilling a 
hole where there is a danger of intersecting a charged or 
misfired hole. 



DISPOSAL OF EXPLOSIVE MATERIALS 



For years the method recommended by the I M E for destroy- 
ing explosives was burning. However, the recent proliferation 
of nonflammable explosive products has caused the IME to 
withdraw this recommendation and its pamphlet that described 



proper burning techniques. The recommendation now made 
by the IME is to contact the nearest explosive distributor, 
whether or not it handles the brand of explosive in question. 
The distributor should dispose of the unwanted explosive. 



PRINCIPAL CAUSES OF BLASTING ACCIDENTS 



Although there is a potential for serious accidents at every 
stage of explosive use, certain aspects of blasting have more 
accident potential than others. Case history articles describing 
typical blasting accidents have been written (2-3). Avoiding 
the following four types of accidents, listed in approximate 
order of frequency, would significantly improve the safety 
record of the blasting industry. 

Improper Guarding. This includes improper guarding of the 
blast area or blasting crew members taking inadequate cover. 
Many people underestimate the potential range of flyrock. 

Impactmg Explosives. Most often this involves drilling into 
holes containing explosives, frequently bootlegs. However, it 
may involve striking explosives with excavator buckets, tracked 



equipment, or rail equipment, or excessive beating on explo- 
sives with a tamping pole. 

Unsafe Cap and Fuse Practices. For various reasons, all 
involving unsafe acts or carelessness, the blaster is still in the 
vicinity of the blast when it detonates. 

Extraneous Electricity. Exposure of electric blasting caps to 
stray ground current, static buildup, radiofrequency energy, 
inductive coupling, or improper test instruments can cause 
unscheduled detonation. Lightning is a hazard with all types of 
explosive materials. 

Other causes of accidents include explosive fires that deto- 
nate (hangfires), poor warning systems, loading hot holes, 
and exposure to blast fumes. 



93 



UNDERGROUND COAL MINE BLASTING 



All underground coal mine blasting is done electrically. The 
foregoing discussion applies to underground coal mine blasting. 
There are additional hazards caused by the potentially explo- 
sive atmosphere present in underground coal mines. Both 
methane and coal dust present an explosion hazard. As a 
result, underground coal mine blasters must undergo rigorous, 



specialized training before they can become qualified shotf irers. 
Because of its specificity, a discussion of underground coal 
mine blasting safety is beyond the scope of this manual. An 
excellent pocket-size pamphlet (4) is available from Hercules, 
Inc., which gives recommended procedures for underground 
coal mine shotfirers. 



REFERENCES 



1. Atlas Powder Co. (Dallas, TX). Handbook of Electric Blasting. 
Rev. 1976,93 pp. 

2. Dick, R. A., and J. G. Gill. Metal and Nonmetal Mine Blasting 
Accidents During 1975-1976. Min. Eng., v. 29, No. 11, November 
1977, pp. 36-39. 

3. . Recent Blasting Fatalities in Metal-Nonmetal Mining. 

Pit and Quarry, v. 67, No. 12, June 1975, pp. 85-87. 

4. Hercules, Inc. (Wilmington, DE). Shotfirer's Guide. 1978, 12 pp. 

5. Institute of Makers of Explosives Safety Library (Washington, 
DC). The American Table of Distances. Pub. No. 2, April 1 977, 1 7 pp. 

6. Do's and Don'ts Instructions and Warnings. Pub. No. 4, 

Rev. July 11, 1978, 12 pp. 

7. Glossary of Industry Terms. Pub. No. 1 2, September 

1981,28 pp. 

8. IME Standard for the Safe Transportation of Electric 

Blasting Caps in the Same Vehicle With Other Explosives. Pub. No. 
22, Mar. 21, 1979, 8 pp. 

9. '. Recommended Industry Safety Standards. Pub. No. 6, 

Feb. 1977,46 pp. 



10. Safety Guide for the Prevention of Radio-Frequency 

Radiation Hazards in the Use of Electric Blasting Caps. Pub. No. 20, 
October 1978, 20 pp. 

1 1 . Safety in the Transportation, Storage, Handling, and 

Use of Explosives. Pub. No. 17, April 1974, 57 pp. 

12. Suggested Code of Regulations for the Manufacture, 

Transportation, Storage, Sale, Possession and Use of Explosive 
Materials. Pub. No. 3, May 1980, 59 pp. 

13. . Typical Storage Magazines. Pub. No. 1, October 

1977,22 pp. 

1 4. National Fire Protection Association (Boston, MA). Manufacture, 
Storage, Transportation and Use of Explosives and Blasting 
Agents— 1973. Pamphlet 495, 1973, 69 pp. 

15. . Separation of Ammonium Nitrate Blasting Agents 

From Explosives— 1976. Pamphlet 492, 1976, 10 pp. 

16. Storage of Ammonium Nitrate— 1975. Pamphlet 490, 

1975,22 pp. 



94 



BIBLIOGRAPHY 



1 . Andrews, A. B. Design of Blasts. Emphasis on Blasting. Ensign 
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2. Ash, R. L. The Mechanics of Rock Breakage, Parts I, II, III, and 

IV. Pit and Quarry, v. 56, No. 2, August 1963, pp. 98-112; No. 3, 
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5, November 1 963, pp. 1 09-1 1 1 , 1 1 4-1 1 8. 

3. Atlas Powder Co. (Dallax TX). Handbook of Electric Blasting. 
Rev. 1976,93 pp. 

4. Pneumatic Loading of Nitro-Carbo-Nitrates; Static Elec- 
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6. Chironis, N. P. New Blasting Machine Permits Custom- 
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7. Condon, J. L., and J. J. Snodgrass. Effects of Primer Type and 
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8. Cook, M. A. Explosives— A Survey of Technical Advances. Ind. 
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10. Damon, G. H., C. M. Mason, N. E. Hanna, and D. R. Forshey. 
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1 1 . Dannenberg, J. Blasthole Dewatering Cuts Costs. Rock Products, 

V. 76, No. 1 2, December 1 973, pp. 66-68. 

1 2. How To Solve Blasting Materials Handling Problems. 

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1 3. Dick, R. A. Explosives and Borehole Loading. Subsection 1 1 .7, 
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14. Factors in Selecting and Applying Commercial Explo- 
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1 7. . Puzzled About Primers for Large Diameter AN-FO 

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8, August 1976, pp. 102-107. 

18. A Review of the Federal Surface Coal Mine Blasting 

Regulations. Proc. 5th Conf. on Explosives and Blasting Technique, 
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Montville, OH, pp. 1-7. 

19. Dick, R. A., and J. G. Gill. Metal and Nonmetal Mine Blasting 
Accidents During 1975-1976. Min. Eng., v. 29, No. 11, November 

1977, pp. 36-39. 

20. Recent Blasting Fatalities in Metal-Nonmetal Mining. 

Pit and Quarry, v. 67, No. 1 2, June 1 975, pp. 85-87. 

21 . Dick, R.A., and J. J. Olson. Choosing the Proper Borehole Size 
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22. Dick, R. A., and D. E. Siskind. Ground Vibration Technology 
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23. Drury, F., and D. J. Westmaas. Considerations Affecting the 
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1978. Society of Explosives Engineers, Montville, OH, pp. 128-153. 

24. E. I. duPontde Nemours & Co., Inc. (Wilmington, DE). Blaster's 
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25. Four Major Methods of Controlled Blasting. 1964, 16 

PP- 

26. Ensign Bickford Co. (Simsbury, CN). Primacord Detonating 
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27. Friend, R. C. Explosives Training Manual. ABA Publishing Co., 
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28. Grant, C. H. Metallized Slurry Boosting: What It Is and How It 
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29. Gregory, C. E. Explosives for North American Engineers. Trans 
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30. Gustaffson, R. Swedish Blasting Technique. SPI, Gothenburg, 
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31 . Hagan, T. N. Optimum Priming for Ammonium Nitrate Fuel-Oil 
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32. Hemphill, G. B. Blasting Operations. McGraw-Hill, New York, 
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33. Hercules, Inc. (Wilmington, DE). Shotfirer's Guide. 1978, 12 
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34. Institute of Makers of Explosives Safety Library (Washington, 
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35. Do's and Don'ts Instructions and Warnings. Pub. No. 

4, Rev. July 1 1 , 1978, 12 pp. 

36. Glossary of Industry Terms. Pub. No. 1 2, September 

1981,28 pp. 

37. IME Standard for the Safe Transportation of Electric 

Blasting Caps in the Same Vehicle With Other Explosives. Pub. 
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38. Recommended Industry Safety Standards. Pub. No. 6, 

February 1 977, 46 pp. 

39. Safety Guide for the Prevention of Radio-Frequency 

Radiation Hazards in the Use of Electric Blasting Caps. Pub. No. 20, 
October 1978, 20 pp. 

40. Safety in the Transportation, Storage, Handling, and 

Use of Explosives. Pub. No. 17, April 1974, 57 pp. 

41 . Suggested Code of Regulations for the Manufac- 
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Materials. Pub. No. 3, May 1980, 59 pp. 

42. . Typical Storage Magazines. Pub. No. 1, October 

1977,22 pp. 

43. Johansson, C. H., and U. Langefors. Methods of Physical 
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44. Junk, N. M. Overburden Blasting Takes on New Dimensions. 
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45. Research on Primers for Blasting Agents. Min. Cong. 

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Characteristics. September 1 972, 37 pp. 

50. National Fire Protection Association (Boston, MA). Manufacture, 
Storage, Transportation and Use of Explosives and Blasting 
Agents— 1973. Pamphlet 495, 1973, 69 pp. 

51. . Separation of Ammonium Nitrate Blasting Agents 

From Explosives— 1976. Pamphlet 492, 1976, 10 pp. 

52. Storage of Ammonium Nitrate— 1 975. Pamphlet 490, 

1975,22 pp. 

53. Nicholls, H. R., C. F. Johnson, and W. I. Duvall. Blasting Vibra- 
tions and Their Effects on Structures. BuMines B 656, 1971, 105 pp. 

54. Porter, D. D. Use of Fragmentation To Evaluate Explosives for 
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95 



55. Pugliese, J. M. Designing Blast Patterns Using Empirical 
Formulas. BuMines IC 8550, 1972, 33 pp. 

56. Robinson, R. V. Water Gel Explosives — Three Generations. 
Canadian Min. and Met. Bull., v. 62, No. 692, December 1969, pp. 
1317-1325. 

57. Schmidt, R. L., R. J. Morrell, D. H. Irby, and R. A. Dick. Applica- 
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7994,1975,25 pp. 

58. Sengupta, D., G. French, M. Heydari, and K. Hanna. The Impact 
of Eliminating Safety Fuse From Metal/Nonmetal Mines (Contract 
J029501 0, Sci. Applications, Inc.). BuMines OFR 61 -81 , August 1 980, 
11 pp.; NTISPB 81-214386. 

59. Siskind, D. E., V. J. Stachura, M. S. Stagg, and J. W. Kopp. 
Structure Response and Damage Produced by Airblast From Surface 
Mining. BuMines Rl 8485, 1980, 111 pp. 

60. Siskind, D. E., M. S. Stagg, J. W. Kopp, and C. H. Dowdlng. 
Structure Response and Damage Produced by Ground Vibration 
From Surface Mine Blasting. BuMines Rl 8507, 1980, 74 pp. 

61 . Siskind, D. E., and C. R. Summers. Blast Noise Standards and 
Instrumentation. BuMines TPR 78, May 1974, 18 pp. 

62. Stachura V. J., D. E. Siskind, and A. J. Engler. Airblast Instru- 
mentation and Measurement Techniques for Surface Mine Blasting. 
BuMines Rl 8508, 1 981 , 53 pp. 



63. Stagg, M. S., and A. J. Engler. Measurement of Blast-Induced 
Ground Vibrations and Seismograph Calibration. BuMines Rl 8506, 
1980,62 pp. 

64. U. S. Bureau of Mines. Apparent Consumption of Industrial 
Explosives and Blasting Agents in the United States, 1981. Mineral 
Industry Survey, June 23, 1982, 12 pp. 

65. U. S. Department of the Treasury; Bureau of Alcohol, Tobacco 
and Firearms. Explosive Materials Regulations. Federal Register, v. 
42, No. 149, Aug. 3, 1977, pp. 39316-39327; Federal Register, v. 45, 
No. 224, Nov. 18, 1980, pp. 76191-76209. 

66. U. S. Mine Enforcement and Safety Administration. Active List 
of Permissible Explosives and Blasting Devices Approved Before 
Dec. 31, 1975. MESA Inf. Rep. 1046, 1976, 10 pp. 

67. U. S. Office of Surface Mining. Surface Coal Mining and Recla- 
mation Operations-Permanent Regulatory Program. Federal Register, 
v. 44, No. 50, Mar. 13, 1979, Book 2, pp. 15404-15406 (regulations). 
Book 3, pp. 15179-15202 (preamble.) 

68. Winzer, S. R. The Firing Times of MS Delay Blasting Caps and 
Their Effect on Blasting Performance. Prepared for National Science 
Foundation (NSF APR 77-05171). Martin Marietta Laboratories 
(Baltimore, MD), June 1 978, 36 pp.; available for consultation at Bureau 
of Mines Twin Cities Research Center, Minneapolis, MN. 



96 



APPENDIX A.— FEDERAL BLASTING REGULATIONS 



Numerous aspects of the manufacture, transportation, storage, 
sale, possession, and use of explosives are regulated. These 
regulations may be enforced at the Federal, State, county, 
city, and township level of government. Some Federal regula- 
tions are enforced by State agencies. State and local agencies 
often adopt regulations that duplicate or expand upon Federal 
regulations. It is important that every person or company 
involved in handling explosives maintains a file of all the 
regulations that appy to the operation. This appendix dis- 
cusses the regulation picture at the Federal level. The powder 
supplier will be able to direct the blaster to the other levels of 
government that enforce regulations in a particular geographic 
area. Where there is a conflict between two regulations in a 
geographic area, the most restrictive, or the one that provides 
the greatest degree of safety, should be complied with. 
Unfortunately, this interpretation is not always clear cut. 

Federal agencies that are specifically chartered by the Code 
of Federal Regulations (CFR) to regulate blasting ; 



1 . Department of Labor 

A. Mine Safety and Health Administration — CFR 30, Parts 
1-199 

B. Occupational Safety and Health Administration — CFR 
29, Parts 1900-1999 



2. Department of Interior, Office of Surface Mining Reclama- 
tion and Enforcement — CFR 30, Parts 700-999 

3. Department of the Treasury, Bureau of Alcohol, Tobacco 
and Firearms— CFR 27, Parts 1 -299 

4. Department of Transportation 

A. Research and Special Programs Administration — CFR 
49, Parts 100-177 

B. Federal Highway Administration — CFR 49, Parts 
301-399 

Table A-1 summarizes the responsibilities of these agencies. 

It is a good idea for the blaster to maintain copies of these 
regulations and to read them. There is a good possibility that 
some of the regulations a blaster may have on hand are out of 
date, because regulations change frequently. The Federal 
Register updates all the regulation changes on a daily basis. 
Codified regulations are updated and published on an annual 
basis. Also, some companies provide the service of keeping 
operators informed of changes in regulations. 



Table A-1. - Federal regulatory agency responsibility 



Department and agency 



Primary responsibility 



Source of regulations 



Department of Labor: 
Mine Safety and Health Administration. 



Onsite safety in the storage, transportation, and use CFR 30, Chapter I: 
of explosives in mining operations. Subchapter C, Parts 15, 16, 17. 

Subchapter D, Parts 24, 25. 
Subchapter H, Part 48. 
Subchapter N, Parts 55. 56, 57. 
Subchapter O, Parts 75, 77 



Occupational Safety and Health 
Administration. 



Onsite safety in the storage, transportation, and use CFR 29, Subtitle B, Chapter XVII: 
of explosives in construction and other nonmine Part 1910, Subpart H. 
blasting operations Part 1 926, Subpart U. 



Department of Interior: Office of Surface Mining 
Reclamation and Enforcement. 



Environmental protection for surface blasting 
associated with coal mines. 



CFR 30, Chapter VII: 
Subchapter K, Parts 816, 817 



Department of Treasury: Bureau of Alcohol, 
Tobacco and Firearms. 



Security in the importation, manufacture, 
distribution, and storage of explosives. 



CFR 27, Part 181: 
Subparts A, B, C, D, E, F, G, H, I, J. 



Department of Transportation: 
Research and Special Projects 
Administration. 



Safe shipment of explosives in interstate 
commerce. 



CFR 49, Chapter I, Subchapter C: 

Parts 171, 172, 173, 174, 175, 176, 177. 



Federal Highway Administration. 



CFR 49, Chapter III, Subchapter B: 
Part 397. 



MINE SAFETY AND HEALTH ADMINISTRATION (MSHA) 



MSHA regulates safety in the handling of explosives in all 
types of mining. Topics included are onsite storage, transporta- 
tion from the magazine to the jobsite, and use. These regula- 
tions can be found in CFR 30, in the following parts: 

Chapter I— Mine Safety and Health Administration 

Subchapter C— Explosives and Related Articles; Tests 
for Permissibility and Suitability 



Part 15 — Explosives and Related Articles (including 

permissible blasting practices) 
Part 16 — Stemming Devices 
Part 1 7— Blasting Devices 

Subchapter D — Electrical Equipment, Lamps, Methane 
Detectors; Tests for Permissibility; Fees 
Part 24— Single-Shot Blasting Units 



97 



Part 25— Multiple-Shot Blasting Units 

Subchapter H — Education and Training 
Part 48 — Training and Retraining of Miners 

Subchapter N — Metal and Nonmetallic Mine Safety and 
Health 
Part 55 — Safety and Health Standards — Metal and Non- 
metallic Open Pit Mines 
55.2 Definitions 
55.6 Explosives 
Part 56 — Safety and Health Standards— Sand, Gravel, 
and Crushed Stone Operations 
56.2 Definitions 
56.6 Explosives 
Part 57— Safety and Health Standards — Metal and Non- 
metallic Underground Mines 



57.2 Definitions 
57.6 Explosives 
57.21 Gassy Mines; 57:21-95—57.21-101, Explosives 

Subchapter — Coal Mine Safety and Health 
Part 75 — Mandatory Safety Standards— 
Underground Coal Mines 
Subpart N — Blasting and Explosives 
Part 77— Mandatory Safety Standards, Surface Coal 
Mines and Surface Work Areas of Under- 
ground Coal Mines 
Subpart N— Explosives and Blasting 
Subpart T— Slope and Shaft Sinking 

In many cases MSHA regulations are enforced by State 
agencies. Some States may have more stringent mine health 
and safety regulations than those of MSHA. 



OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION (OSHA) 



OSHA is a companion agency of MSHA, both being in the 
Department of Labor. OSHA regulates safety in the handling 
of explosives in nonmining industries, most notably construction. 
The OSHA blasting regulations are found in CFR 29, in the 
following parts: 

Subtitle B — Regulations Relating to Labor 

Chapter XVII— OSHA, Department of Labor 
Subpart H — Hazardous Materials 



1910.109 — Explosives and Blasting Agents 

Part 1926— Safety and Health Regulations for 

Construction 
Subpart U — Blasting and Use of Explosives (Sections 
1926.900—1926.914) 

In many cases, OSHA regulations are enforced by State 
agencies. Some States may have more stringent health and 
safety regulations for construction than OSHA. 



OFFICE OF SURFACE MINING RECLAMATION AND ENFORCEMENT (OSM) 



OSM regulations are the most recent Federal blasting 
regulations, having been promulgated in 1979 (67).'^ These 
regulations, which deal only with surface coal mines and sur- 
face operations associated with underground coal mines, are 
environmental in nature. There are no Federal environmental 
regulations for metal-nonmetal mines. The OSM blasting regula- 
tions are designed to protect persons and property outside the 
mine area from potentially harmful effects of blasting. They 
deal with blaster qualifications, preblasting surveys, blasting 
schedules, control of ground vibrations and airblast, seismo- 
graphic measurements, and blast records. The OSM regula- 
tions are found in CFR 30, in the following parts: 



Chapter VII — OSM, Department of the Interior 

Subchapter K — Permanent Program Performance 
Standards 
Part 816 — Surface Mining Activities 

Sections 81 6.61 — 81 6.68, Use of Explosives 
Part 817 — Underground Mining Activities 

Sections 81 7.61— 81 7.68, Use of Explosives 

In most cases, OSM regulations are enforced by the individ- 
ual States. Some of these States may have more stringent 
environmental regulations than those of OSM. 



BUREAU OF ALCOHOL TOBACCO AND FIREARMS (BATF) 



BATF regulates security in the importation, manufacture, 
distribution, and storage of explosives. The primary goal of 
BATF is to prevent explosives from being used by unautho- 
rized persons. Recordkeeping and secure storage are key 
requirements of the regulations. BATF has published updates 
of these regulations (65). 



^Italicized numbers in parentheses refer to items in the bibliography 
preceding the appendixes. 



The BATF regulations are found in CFR 27, Part 1 81 , Subparts 
A through J, as follows: 



Subpart A— Introduction 

Subpart B — Definitions 

Subpart C — Administrative and Miscellaneous Proceedings 

Subpart D — Licenses and Permits 

Subpart E — License and Permit Proceedings 

Subpart F— Conduct of Business or Operations 

Subpart G— Records and Reports 



Subpart H — Exemptions 

Subpart I — Unlawful Acts, Penalties, Seizures, and Forfeitures 

Subpart J — Storage 



Subpart G, Records and Reports, and Subpart J, Storage, 
are enforced by MSHA under a memorandum of understand- 
ing with BATF. BATF enforces the remainder of the regulations. 



DEPARTMENT OF TRANSPORTATION (DOT) 



DOT regulates the safe shipment of explosives in interstate 
commerce, including proper identification, packaging, public 
protection, and transportation vehicles. Many State and local 
agencies have adopted equal or more stringent regulations for 
transportion of explosives within their jurisdiction. The DOT 
regulations are found in CFR 49, Chapters I and III, as follows: 

Chapter I — Research and Special Programs Administration 

Subchapter C — Hazardous Material Regulations 

Part 171 — General Information, Regulations, and 
Definitions 

Part 1 72 — Hazardous Materials Table and Hazard- 
ous Materials Communication Regulations 

Part 1 73 — Shipper-General Requirements for Ship- 
ments and Packaging 

Part 1 74 — Carriage by Rail 

Part 1 75 — Carriage by Aircraft 

Part 1 76— Carriage by Vessel 



Part 1 77— Carriage by Public Highway 
Chapter III— Federal Highway Administration 
Subchapter B— Motor Carrier Safety Regulations 
Part 397— Transportation of Hazardous Materials: 
Driving and Parking Rules 

No attempt has been made here to analyze or interpret the 
regulations cited in this appendix. It is important that every 
blaster has access to and reads these regulations to make 
sure that he or she is in compliance with them. Interpretation of 
regulations is often a difficult process. Where a blaster is not 
sure exactly how a regulation pertains to his or her operation, 
an interpretation should be obtained from a representative of 
the regulatory agency. 

In addition to these specific blasting regulations, blasting 
operations are also governed by other regulations that apply 
across the board to all industries, such as air quality control 
and nuisance noise. 



APPENDIX B.— GLOSSARY OF TERMS USED IN EXPLOSIVES AND BLASTING^ 



Acoustical impedance.— The mathematical expression char- 
acterizing a material as to its energy transfer properties. The 
product of its unit density and its sonic velocity. 

Adobe ctiarge.—See mud cap. 

Airblast— An airbome shock wave resulting from the detona- 
tion of explosives. May be caused by burden movement or the 
release of expanding gas into the air. Airblast may or may not 
be audible. 

Mrdox.—A system that uses 10,000 psi compressed air to 
break undercut coal. Airdox will not ignite a gassy or dusty 
atmosphere. 

Aluminum.— A metal commonly used as a fuel or sensitizing 
agent in explosives and blasting agents. Normally used in 
finely divided particle or flake form. 

American Table of Distances.— A quantity-distance table 
published by IME as pamphlet No. 2, which specifies safe 
explosive storage distances from inhabited buildings, public 
highways, passenger railways and other stored explosive 
materials. 

Ammonium nitrate (AN).— The most commonly used oxidizer 
in explosives and blasting agents. Its formula is NH4NO3. 

AN-FO.—An explosive material consisting of ammonium 
nitrate and fuel oil. The most commonly used blasting agent. 

Axial priming.— A system for priming blasting agents in 
which a core of priming material extends through most or all of 
the blasting agent charge length. 



Back break.— Rock broken beyond the limits of the last row 
of holes. 

Back holes.— The top holes in a tunnel or drift round. 

Base charge.— The main explosive charge in a detonator. 

BATF.— Bureau of Alcohol, Tobacco and Firearms, U.S. 
Department of the Treasury, which enforces explosives con- 
trol and security regulations. 

Beds or bedding.— Layers of sedimentary rock, usually 
separated by a surface of discontinuity. As a rule, the rock can 
be readily separated along these planes. 

Bench.— The horizontal ledge in a quarry face along which 
holes are drilled vertically. Benching is the process of excavat- 
ing whereby terraces or ledges are worked in a stepped 
sequence. 

Binary explosive.— Ar) explosive based on two nonexplo- 
sive ingredients, such as nitromethane and ammonium nitrate, 
which are shipped and stored separately and mixed at the 
jobsite to form a high explosive. 

Black powder.— A low explosive consisting of sodium or 
potassium nitrate, carbon, and sulfur. Black powder is seldom 
used today because of its low energy, poor fume quality, and 
extreme sensitivity to sparks. 

Blast— The detonation of explosives to break rock. 

Blast area.— The area near a blast within the influence of 
flying rock missiles, or concussion. 

Blaster.— A qualified person in charge of a blast. Also, a 
person (blaster-in-charge) who has passisd a test, approved 
by OSM, which certifies his or her qualifications to supervise 
blasting activities. 



^Additional definitions can be found in Institute of Makers of Explo- 
sives Pamphlet No. 1 2, Glossary of Industry Terms, September 1 981 , 
28 pp. 



Blasters' galvanometer; blasters' multimeter.—See galva- 
nometer; multimeter. 

Blasthoie.—A hole drilled in rock or other material for the 
placement of explosives. 

Blasting agent.— An explosive that meets prescribed cri- 
teria for insensitivity to initiation. For storage, any material or 
mixture consisting of a fuel and oxidizer, intended for blasting, 
not othenwise defined as an explosive, provided that the fin- 
ished product, as mixed and packaged for use or shipment, 
cannot be detonated by means of a No. 8 test blasting cap 
when unconfined (BATF). For transportation, a material designed 
for blasting which has been tested in accordance with CFR 49, 
Section 173.14a, and found to be so insensitive that there is 
very little probability of accidental initiation to explosion or 
transition from deflagration to detonation (DOT). 

Blasting cap.— A detonator that is initiated by safety fuse 
(MSHA). See also detonator. 

Blasting circuit.-The electrical circuit used to fire one or 
more electric blasting caps. 

Blasting crew.— A group of persons whose purpose is to 
load explosive charges. 

Blasting machine.— Any machine built expressly for the 
purpose of energizing electric blasting caps or other types of 
initiator. 

Blasting mat.— See mat. 

Blasting switch.— A switch used to connect a power source 
to a blasting circuit. 

Blistering.— See mud cap. 

Blockhole.—A hole drilled into a boulder to allow the place- 
ment of a small charge to break the boulder. 

Booster.— A unit of explosive or blasting agent used for 
perpetuating or intensifying an explosive reaction. A booster 
does not contain an initiating device but is often cap sensitive. 

Soof/eg.— That portion of a borehole that remains relatively 
intact after having been charged with explosive and fired. A 
bootleg may contain unfired explosive and should be consid- 
ered hazardous. 

Borehole (blasthole).—A drilled hole, usually in rock, into 
which explosives are loaded for blasting. 

Borehole pressure.— The pressure which the hot gases of 
detonation exert on the borehole wall. Borehole pressure is 
primarily a function of the density of the explosive and the heat 
of explosion. 

Bridge wire.— A very fine filament wire imbedded in the 
ignition element of an electric blasting cap. An electric current 
passing through the wire causes a sudden heat rise, causing 
the ignition element to be ignited. 

Brisance.—A property of an explosive roughly equivalent to 
detonation velocity. An explosive with a high detonation veloc- 
ity has high brisance. 

Bubble energy.— The expanding gas energy of an explosive, 
as measured in an underwater test. 

Bulk mix.— A mass of explosive material prepared for use 
without packaging. 

Bulk strength. —The strength of an explosive per unit volume. 

Bulldoze.— See mud cap. 

Burden.— The distance from an explosive charge to the 
nearest free or open face. Technically, there may be an appar- 
ent burden and a true burden, the latter being measured in the 
direction in which displacement of broken rock will occur follow- 
ing firing of the explosive charge. Also, the amount of material 
to be blasted by a given hole, given in tons or cubic yards. 



100 



Burn cut— A parallel hole cut employing several closely 
spaced blastholes. Not all of the holes are loaded with explosive. 
The cut creates a cylindrical opening by shattering the rock. 

Bus wires.— The two wires, joined to the connecting wire, to 
which the leg wires of the electric caps are connected in a 
parallel circuit. Each leg wire of each cap is connected to a 
different bus wire. In a series-in-parallel circuit, each end of 
each series is connected to a different bus wire. 

Butt.— See bootleg. 



Cap.— See detonator. 

Capped fuse.— A length of safety fuse to which a blasting 
cap has been attached. 

Capped primer.— A package or cartridge of cap-sensitive 
explosive which is specifically designed to transmit detonation 
to other explosives and which contains a detonator (MSHA). 

Cap sensitivity.— The sensitivity of an explosive to initiation, 
expressed in terms of an IME No. 8 test detonator or a fraction 
thereof. 

Carbon monoxide.— A poisonous gas created by detonat- 
ing explosive materials. Excessive carbon monoxide is caused 
by an inadequate amount of oxygen in the explosive mixture 
(excessive fuel). 

Cardox.—A system that uses a cartridge filled with liquid 
carbon dioxide, which, when initiated by a mixture of potas- 
sium perchlorate and charcoal, creates a pressure adequate 
to break undercut coal. 

Cartridge.— A rigid or semirigid container of explosive or 
blasting agent of a specified length or diameter. 

Cartridge count— The number of 1 V^- by 8-in cartridges of 
explosives per 50-lb case. 

Cartridge strength.— A rating that compares a given vol- 
ume of explosive with an equivalent volume of straight nitro- 
glycerin dynamite, expressed as a percentage. 

Cast primer.— A cast unit of explosive, usually pentolite or 
composition B, commonly used to initiate detonation in a 
blasting agent. 

Chambering.— The process of enlarging a portion of blasthole 
(usually the bottom) by firing a series of small explosive charges. 
Chambering can also be done by mechanical or thermal 
methods. 

Chapman-Jouguet (C-J) plane.— \n a detonating explosive 
column, the plane that defines the rear boundary of the pri- 
mary reaction zone. 

Circuit tester.— See galvanometer; multimeter. 

Class A explosive.— Defined by the U.S. Department of 
Transportation (DOT) as an explosive that possesses detonat- 
ing or otherwise maximum hazard; such as, but not limited to, 
dynamite, nitroglycerin, lead azide, black powder, blasting 
caps, and detonating primers. 

Class B exp/os/Ve.— Defined by DOT as an explosive that 
possesses flammable hazard; such as, but not limited to, 
propellant explosives, photographic flash powders, and some 
special fireworks. 

Class C explosive.— Defmed by DOT as an explosive that 
contains Class A or Class B explosives, or both, as compo- 
nents but in restricted quantities. For example, blasting caps 
or electric blasting caps in lots of less than 1 ,000. 

Co//ar.— The mouth or opening of a borehole or shaft. To 
collar in drilling means the act of starting a borehole. 

Collar distance.— The distance from the top of the powder 
column to the collar of the blasthole, usually filled with stemming. 

Column charge.— A long, continuous charge of explosive or 
blasting agent in a borehole. 



Commercial explosives.— Explosives designed and used 
for commercial or industrial, rather than military applications. 

Composition B.—A mixture of RDX and TNT which, when 
cast, has a density of 1 .65 g/cu cm and a velocity of 25,000 fps. 
It is useful as a primer for blasting agents. 

Condenser-discharge blasting machine.— A blasting machine 
that uses battehes or magnets to energize one or more con- 
densers (capacitors) whose stored energy is released into a 
blasting circuit. 

Confined detonation velocity.— The detonation velocity of 
an explosive or blasting agent under confinement, such as in a 
borehole. 

Connecting wire.— A wire, smaller in gage than the lead 
wire, used in a blasting circuit to connect the cap circuit with 
the lead wire or to extend leg wires from one borehole to 
another. Usually considered expendable. 

Con/iecfor.— See MS connector. 

Controlled b/asf/ng.— Techniques used to control overbreak 
and produce a competent final excavation wall. See line drilling, 
presplitting, smooth blasting, and cushion blasting. 

Cordeau detonant fuse.— A term used to define detonating 
cord. 

Cornish cut.— See parallel hole cut. 

Coromant cut.— See parallel hole cut. 

Coupling.— The degree to which an explosive fills the borehole. 
Bulk loaded explosives are completely coupled. Untamped 
cartridges are decoupled. Also, capacitive and inductive cou- 
pling from powerlines, which may be introduced into an elec- 
tric blasting circuit. 

Coyote blasting.— The practice of dhving tunnels horizon- 
tally into a rock face at the foot of the shot. Explosives are 
loaded into these tunnels. Coyote blasting is used where it is 
impractical to drill vertically. 

Critical diameter.— For any explosive, the minimum diame- 
ter for propagation of a stable detonation. Critical diameter is 
affected by confinement, temperature, and pressure on the 
explosive. 

Crosslinking agent.— The final ingredient added to a water 
gel or slurry, causing it to change from a liquid to a gel. 

Current limiting device.— A device used to prevent arcing in 
electric blasting caps by limiting the amount or duration of 
current flow. Also used in a blasters' galvanometer or multime- 
ter to assure a safe current output. 

Cushion blasting.— A surface blasting technique used to 
produce competent slopes. The cushion holes, fired after the 
main charge, have a reduced spacing and employ decoupled 
charges. 

Cushion stick.— A cartridge of explosive loaded into a small- 
diameter borehole before the primer. The use of a cushion 
stick is not generally recommended because of possible result- 
ing bootlegs. 

Cut.— An arrangement of holes used in underground mining 
and tunnel blasting to provide a free face to which the remain- 
der of the round can break. Also the opening created by the cut 
holes. 

Cutoffs.— A portion of a column of explosives that has failed 
to detonate owing to bridging or a shifting of the rock formation, 
often due to an improper delay system. Also a cessation of 
detonation in detonating cord. 



Dead press/ng.— Desensitization of an explosive, caused 
by pressurization. Tiny air bubbles, required for sensitivity, are 
literally squeezed from the mixture. 

Dec/£>e/.— The unit of sound pressure commonly used to 



101 



measure airblast from explosives. The decibel scale is 
logarithmic. 

Deck.— A small charge or portion of a blasthole loaded with 
explosives which is separated from other charges by stem- 
ming or an air cushion. 

Decoupling.— The use of cartridged products significantly 
smaller in diameter than the borehole. Decoupled charges are 
normally not used except in cushion blasting, smooth blasting, 
presplitting, and other situations where crushing is undesirable. 

Deflagration.— A subsonic but extremely rapid explosive 
reaction accompanied by gas formation and borehole pressure, 
but without shock. 

Delay blasting.— The use of delay detonators or connectors 
that cause separate charges to detonate at different times, 
rather than simultaneously. 

Delay connector.— A nonelectric, short-interval delay device 
for use in delaying blasts that are initiated by detonating cord. 

Delay detonator.— A detonator, either electric or nonelectric, 
with a built-in element that creates a delay between the input 
of energy and the explosion of the detonator. 

Delay electric blasting cap.— An electric blasting cap with a 
built-in delay that delays cap detonation in predetermined time 
intervals, from milliseconds up to a second or more, between 
successive delays. 

Delay element— Thai portion of a blasting cap which causes 
a delay between the instant of application of energy to the cap 
and the time of detonation of the base charge of the cap. 

Density.— The weight per unit volume of explosive, expressed 
as cartridge count or grams per cubic centimeter. See loading 
density. 

Department of Transportation (DOT).— A Federal agency 
that regulates safety in interstate shipping of explosives and 
other hazardous materials. 

Detaline System.— A nonelectric system for initiating blast- 
ing caps in which the energy is transmitted through the circuit 
by means of a low-energy detonating cord. 

Detonating cord.— A plastic-covered core of high-velocity 
explosive, usually PETN, used to detonate charges of explosives. 
The plastic covering, in turn, is covered with various combina- 
tions of textiles and waterproofing. 

Detonation.— A supersonic explosive reaction that propa- 
gates a shock wave through the explosive accompanied by a 
chemical reaction that furnishes energy to sustain the shock 
wave propagation in a stable manner. Detonation creates both 
a detonation pressure and a borehole pressure. 

Detonation pressure.— The head-on pressure created by 
the detonation proceeding down the explosive column. Detona- 
tion pressure is a function of the explosive's density and the 
square of its velocity. 

Detonation velocity.— See velocity. 

Detonator.— Any device containing a detonating charge that 
is used to initiate an explosive. Includes, but is not limited to, 
blasting caps, electric blasting caps, and nonelectric instanta- 
neous or delay blasting caps. 

Ditch blasting.—See propagation blasting. 

DOT.— See Department of Transportation. 

Downline.— The line of detonating cord in the borehole 
which transmits energy from the trunkline down the hole to the 
primer. 

Drilling pattern.— See pattern. 

Drop ball.— Known also as a headache ball. An iron or steel 
weight held on a wire rope which is dropped from a height onto 
large boulders for the purpose of breaking them into smaller 
fragments. 

Dynam/fe.— The high explosive invented by Alfred Nobel. 



Any high explosive in which the sensitizer is nitroglycerin or a 
similar explosive oil. 



Echelon pattern.— A delay pattem that causes the true burden, 
at the time of detonation, to be at an oblique angle from the 
original free face. 

Electric blasting cap.— A blasting cap designed to be initi- 
ated by an electric current. 

Electric stomi.— An atmospheric disturbance of intense electri- 
cal activity presenting a hazard in all blasting activities. 

Emulsion.— An explosive material containing substantial 
amounts of oxidizers dissolved in water droplets surrounded 
by an immiscible fuel. Similar to a slurry in some respects. 

Exploding bridge wire (EBW).—A wire that explodes upon 
application of current. It takes the place of the primary explo- 
sive in an electric detonator. An exploding bridge wire detona- 
tor is an electric detonator that employs an exploding bridge 
wire rather than a primary explosive. An exploding bridge wire 
detonator functions instantaneously. 

Explosion.— A thermochemical process in which mixtures 
of gases, solids, or liquids react with the almost instantaneous 
formation of gaseous pressures and sudden heat release. 

Explosion pressure.— See borehole pressure. 

Explosive.— Any chemical mixture that reacts at high veloc- 
ity to liberate gas and heat, causing very high pressures. 
BATF classifications include high explosives and low explosives. 
Also, any substance classified as an explosive by DOT. 

Explosive materials.— A term which includes, but is not 
necessarily limited to, dynamite and other high explosives, 
slurries, water gels, emulsions, blasting agents, black powder, 
pellet powder, initiating explosives, detonators, safety fuses, 
squibs, detonating cord, igniter cord, and igniters. 

Extra dynamite.— A\so called ammonia dynamite, a dyna- 
mite that derives the major portion of its energy from ammo- 
nium nitrate. 

Extraneous electricity.— E\ec\nca\ energy, other than actual 
firing current, which may be a hazard with electric blasting 
caps. Includes stray current, static electricity, lightning, radio- 
frequency energy, and capacitive or inductive coupling. 



Face.— A rock surface exposed to air. Also called a free 
face, a face provides the rock with room to expand upon 
fragmentation. 

Firing current.— E\ecinc current purposely introduced into a 
blasting circuit for the purpose of initiation. Also, the amount of 
current required to activate an electric blasting cap. 

Firing line.— A line, often permanent, extending from the 
firing location to the electric blasting cap circuit. Also called 
lead wire. 

Flash over.— Sympathetic detonation between explosive 
charges or between charged blastholes. 

F/yroc/c.— Rock that is propelled through the air from a blast. 
Excessive flyrock may be caused by poor blast design or 
unexpected zones of weakness in thn rock. 

Fracturing.— The breaking of rock with or without move- 
ment of the broken pieces. 

Fragmentation.— The extent to which a rock is broken into 
pieces by blasting. Also the act of breaking rock. 

Fuel.— An ingredient in an explosive which reacts with an 
oxidizer to form gaseous products of detonation. 

Fuel oil.— The fuel, usually No. 2 diesel fuel, in AN-FO. 

Fume classification.— An IME quantification of the amount 
of fumes generated by an explosive or blasting agent. 



102 



Fume quality.— A measure of the toxic fumes to be expected 
when a specific explosive is properly detonated. See fumes. 

Fumes.— Noxious or poisonous gases lilierated from a blast. 
May be due to a low fume quality explosive or inefficient 
detonation. 

Fuse.— See safety fuse. 

Fuse lighter.— A pyrotechnic device for rapid and depend- 
able lighting of safety fuse. 



Ga/vanometer.- (More properly called blasters' galva- 
nometer.) A measuring instrument containing a silver chloride 
cell and/or a current limiting device which is used to measure 
resistance in an electric blasting circuit. Only a device specific- 
ally identified as a blasting galvanometer or blasting multime- 
ter should be used for this purpose. 

Gap sensitivity.— A measure of the distance across which 
an explosive can propagate a detonation. The gap may be air 
or a defined solid material. Gap sensitivity is a measure of the 
likelihood of sympathetic propagation. 

Gas detonation system.— A system for initiating caps in 
which the energy is transmitted through the circuit by means of 
a gas detonation inside a hollow plastic tube. 

Gelatin.— An explosive or blasting agent that has a gelati- 
nous consistency. The term is usually applied to a gelatin 
dynamite but may also be a water gel. 

Gelatin dynamite.— A highly water-resistant dynamite with 
a gelatinous consistency. 

Generator blasting machine.— A blasting machine oper- 
ated by vigorously pushing down a rack bar or twisting a 
handle. Now largely replaced by condenser discharge blast- 
ing machines. 

Grains.— A system of weight measurement in which 7,000 
grains equal 1 lb. 

Ground vibration.— A shaking of the ground caused by the 
elastic wave emanating from a blast. Excessive vibrations 
may cause damage to structures. 



Hangfire.—Jhe detonation of an explosive charge at a time 
after its designed firing time. A source of serious accidents. 

Heading.— A horizontal excavation driven in an underground 
mine. 

Hercudet.—See gas detonation system. 

Hertz.— A term used to express the frequency of ground 
vibrations and airblast. One hertz is one cycle per s eco nd. 

High explosive.— Any product used in blastTng which Ts 
sensitive to a No. 8 test blasting cap and reacts at a speed 
faster than that of sound in the explosive medium. A classifica- 
tion used by BATF for explosive storage. 

H/gf/7wa//.— The bench, bluff, or ledge on the edge of a 
surface excavation. This term is most commonly used in coal 
strip mining. 



Ignitacord.—A cordlike fuse that burns progressively along 
its length with an external flame at the zone of burning and is 
used for lighting a series of safety fuses in sequence. Burns 
with a spitting flame similar to a Fourth-of-July sparkler. 

IME.— The Institute of Makers of Exptosives. A trade organiza- 
tion dealing with the use of explosives, concerned with safety 
in manufacture, transportation, storage, handling, and use. 
The IME publishes a series of blasting safety pamphlets. 

Initiation.— The act of detonating a high explosive by means 
of a cap, a mechanical device, or other means. Also the act of 
detonating the initiator. 



Instantaneous detonator.— A detonator that contains no 
delay element. 



Jet loader.— A system for loading AN-FO into small blastholes 
in which the AN-FO is drawn from a container by the venturi 
principle and blown into the hole at high velocity through a 
semiconductive loading hose. 

Jo/nte.— Planes within a rock mass along which there is no 
resistance to separation and along which there has been no 
relative movement of the material on either side. Joints occur 
in sets, the planes of which may be mutually perpendicular. 
Joints are often called partings. 

Jumbo.— A machine designed to contain two or more mounted 
drilling units that may or may not be operated independently. 



Kerf.— A slot cut in a coal or soft rock face by a mechanical 
cutter to provide a free face for blasting. 



Lead wire.— The wire connecting the electrical power source 
with the leg wires or connecting wires of a blasting circuit. Also 
called firing line. 

LEDC— Low energy detonating cord, which may be used to 
initiate nonelectric blasting caps. 

Leg w/res.— Wires connected to the bridge wire of an elec- 
tric blasting cap and extending from the waterproof plug. The 
opposite ends are used to connect the cap into a circuit. 

Zj/ifers.— The bottom holes in a tunnel or drift round. 

Line drilling.— A method of overbreak control in which a 
series of very closely spaced holes are drilled at the perimeter 
of the excavation. These holes are not loaded with explosive. 

Liquid oxygen explosive.— A high explosive made by soak- 
ing cartridges of carbonaceous materials in liquid oxygen. 
This explosive is rarely used today. 

Loading density.— An expression of explosive density in 
terms of pounds of explosive per foot of charge of a specific 
diameter. 

Loading factor.— See powder factor. 

Loading pole.— A pole made of nonsparking material, used 
to push explosive cartridges into a borehole and to break and 
tightly pack the explosive cartridges into the hole. 

Low explosive.— An explosive in which the speed of reac- 
tion is slower than the speed of sound, such as black powder. 
A classification used by BATF for explosive storage. 

LOX.— See liquid oxygen explosive. 



Magazine.— A building, structure, or container specially con- 
structed for storing explosives, blasting agents, detonators, or 
other explosive materials. 

Mat.— A covering placed over a shot to hold down flying 
material; usually made of woven wire cable, rope, or scrap 
tires. 

Maximum firing current.— The highest current (amperage) 
recommended for the safe and effective performance of an 
electric blasting cap. 

/Wera///zed.— Sensitized or energized with finely divided metal 
flakes, powders, or granules, usually aluminum. 

Michigan cut.— See parallel hole cut. 

Microballoons.— Tiny hollow spheres of glass or plastic 
which are added to explosive materials to enhance sensitivity 
by assuring an adequate content of entrapped air. 

Millisecond.— The unit of measurement of short delay 
intervals, equal to 1/1000 of a second. 



103 



Millisecond delay caps.— Delay detonators that have built-in 
time delays of various lengths. The interval between the delays 
at the lower end of the series is usually 25 ms. The interval 
between delays at the upper end of the series may be 100 to 
300 ms. 

Minimum firing current.— The lowest current (amperage) 
that will initiate an electric blasting cap within a specified short 
interval of time. 

Misfire.— A charge, or part of a charge, which for any reason 
has failed to fire as planned. All misfires are dangerous. 

Monomethylaminenitrate.—A compound used to sensitize 
some water gels. 

MS connector.— A device used as a delay in a detonating 
cord circuit connecting one hole in the circuit with another or 
one row of holes to other rows of holes. 

MSHA.— The Mine Safety and Health Administration. An 
agency under the Department of Labor which enforces health 
and safety regulations in the mining industry. 

Muckpile.—A pile of broken rock or dirt that is to be loaded 
for removal. 

Mud cap.— Referred to also as adobe, bulldoze, blistering, 
or plaster shot. A charge of explosive fired in contact with the 
surface of a rock, usually covered with a quantity of mud, wet 
earth, or similar substance. No borehole is used. 

Multimeter.— {More properly called blasters' multimeter.) A 
multipurpose test instrument used to check line voltages, firing 
circuits, current leakage, stray currents, and other measure- 
ments pertinent to electric blasting. Only a meter specifically 
designated as a blasters' multimeter or blasters' galvanome- 
ter should be used to test electric blasting circuits. 



National Fire Protection Association (NFPA).— An industry- 
government association that publishes standards for explo- 
sive material and ammonium nitrate. 

Nitrocarbonitrate.—A classification once given to a blasting 
agent by DOT for shipping purposes. This term is now obsolete. 

Nitrogen ox/c/es.- Poisonous gases created by detonating 
explosive materials. Excessive nitrogen oxides may be caused 
by an excessive amount of oxygen in the explosive mixture 
(excessive oxidizer), or by inefficient detonation. 

Nitroglycerin (NG).— The explosive oil originally used as 
the sensitizer in dynamites, represented by the formula 

C3H5(ON02)3. 

Nitromethane.—A liquid compound used as a fuel in two- 
component (binary) explosives and as rocket fuel. 

Nitropropane.-A liquid fuel that can be combined with 
pulverized ammonium nitrate prills to make a dense blasting 
mixture. 

Nitrostarch.—A solid explosive, similar to nitroglycerin in 
function, used as the base of "nonheadache" powders. 

Nonel.—See shock tube system. 

Nonelectric delay blasting cap.— A detonator with a delay 
element, capable of being initiated nonelectrically. See shock 
tube system; gas detonation system; Detaline System. 

No. 8 test blasting cap.— See test blasting cap No. 8. 



OSHA.— The Occupational Safety and Health Administration. 
An agency under the Department of Labor which enforces 
health and safety regulations in the construction industry, 
including blasting. 

OSM.— The Office of Surface Mining Reclamation and 
Enforcement. An agency under the Department of Interior 
which enforces surface environmental regulations in the coal 
mining industry. 



Overtorea/c.— Excessive breakage of rock beyond the desired 
excavation limit. 

Overbt/rofen.— Worthless material lying on top of a deposit 
of useful materials. Overburden often refers to dirt or gravel, 
but can be rock, such as shale over limestone or shale and 
limestone over coal. 

Overdrive.— The act of inducing a velocity higher than the 
steady state velocity in a powder column by the use of a 
powerful primer. Overdrive is a temporary phenomenon and 
the powder quickly assumes its steady state velocity. 

Oxides of nitrogen.— See nitrogen oxides. 

Oxidizer.— An ingredient in an explosive or blasting agent 
which supplies oxygen to combine with the fuel to form gas- 
eous or solid products of detonation. Ammonium nitrate is the 
most common oxidizer used in commercial explosives. 

Oxygen balance.— A state of equilibrium in a mixture of 
fuels and oxidizers at which the gaseous products of detona- 
tion are predominately carbon dioxide, water vapor (steam), 
and free nitrogen. A mixture containing excess oxygen has a 
positive oxygen balance. One with excess fuel has a negative 
oxygen balance. 



Parallel circuit— A circuit in which two wires, called bus 
wires, extend from the lead wire. One leg wire from each cap in 
the circuit is hooked to each of the bus wires. 

Parallel hole cut.— A group of parallel holes, some of which 
are loaded with explosives, used to establish a free face in 
tunnel or heading blasting. One or more of the unloaded holes 
may be larger than the blastholes. Also called Coromant, 
Cornish, burn, shatter, or Michigan cut. 

Parallel series c/rcu/f.— Similar to a parallel circuit, but involv- 
ing two or more series of electric blasting caps. One end of 
each series of caps is connected to each of the bus wires. 
Sometimes called series-in-parallel circuit. 

Particle velocity.— A measure of ground vibration. Describes 
the velocity at which a particle of ground vibrates when excited 
by a seismic wave. 

Pattern.— A plan of holes laid out on a face or bench which 
are to be drilled for blasting. Burden and spacing dimensions 
are usually expressed in feet. 

Pe//efpoivGfer.— Black powder pressed into 2-in-long, 174- 
in to 2-in diameter cylindrical pellets. 

Pentaerythritoltetranitrate (PETN).—A military explosive 
compound used as the core load of detonating cord and the 
base charge of blasting caps. 

Pentolite.—A mixture of PETN and TNT which, when cast, is 
used as a cast primer. 

Permissible.— A machine, material, apparatus, or device 
that has been investigated, tested, and approved by the Bureau 
of Mines or MSHA, and is maintained in permissible condition 
(MSHA). 

Permissible b/asftng.— Blasting according to MSHA regula- 
tions for underground coal mines or other gassy underground 
mines. 

Permissible exp/os/Ves.— Explosives that have been approved 
by MSHA for use in underground coal mines or other gassy 
mines. 

PETN.— See pentaerythritoltetranitrate. 

P/acarofs.— Signs placed on vehicles transporting hazard- 
ous materials, including explosives, indicating the nature of 
the cargo. 

Plaster shot.— See mud cap. 

Pneumatic loader. — One of a variety of machines, powered 
by compressed air, used to load bulk blasting agents or cartridged 
water gels. 



104 



Powder.— Any solid explosive. 

Powder chest— A substantial, nonconductive portable con- 
tainer equipped with a lid and used at blasting sites for tempo- 
rary storage of explosives. 

Powder factor.— A ratio between the amount of powder 
loaded and the amount of rock broken, usually expressed as 
pounds per ton or pounds per cubic yard. In some cases, the 
reciprocals of these terms are used. 

Preblast survey.— A documentation of the existing condi- 
tion of a structure. The survey is used to determine whether 
subsequent blasting causes damage to the structure. 

Premature.— A charge that detonates before it is intended. 
Prematures can be hazardous. 

Preshearing.—See presplitting. 

Presplitting.—A form of controlled blasting in which decou- 
pled charges are fired in closely spaced holes at the perimeter 
of the excavation. A presplit blast is fired before the main blast. 
Also called preshearing. 

Pressure vessel.— A system for loading AN-FO into small- 
diameter blastholes. The AN-FO is contained in a sealed 
vessel, to which air pressure is applied, forcing the AN-FO 
through a semiconductive hose and into the blasthole. Also 
known as pressure pot. 

Prill.— \n blasting, a small porous sphere of ammonium 
nitrate capable of absorbing more than 6 pet by weight of fuel 
oil. Blasting prills have a bulk density of 0.80 to 0.85 g/cu cm. 

Primary blast.— The main blast executed to sustain production. 

Primary explosive.— An explosive or explosive mixture, sensi- 
tive to spark, flame, impact or friction, used in a detonator to 
initiate the explosion. 

Primer.— A unit, package, or cartridge of cap-sensitive explo- 
sive used to initiate other explosives or blasting agents and 
which contains a detonator (MSHA). 

Propagation.— The detonation of explosive charges by an 
impulse from a nearby explosive charge. 

Propagation blasting.— The use of closely spaced, sensi- 
tive charges. The shock from the first charge propagates 
through the ground, setting off the adjacent charge, and so on. 
Only one detonator is required. Primarily used for ditching in 
damp ground. 

Propellant explosive.— An explosive that normally defla- 
grates and is used for propulsion. 

Pull.— The quantity of rock or length of advance excavated 
by a blast round. 



Radiofrequency energy.— Electrical energy traveling through 
the air as radio or electromagnetic waves. Under ideal conditions, 
this energy can fire an electric blasting cap. IME Pamphlet No. 
20 recommends safe distances from transmitters to electric 
blasting caps. 

Radiofrequency transmitter.— An electric device, such as a 
stationary or mobile radio transmitting station, which transmits 
a radiofrequency wave. 

f?DX.— Cyclotrimethylenetrinitramine, an explosive substance 
used in the manufacture of compositions B, C-3, and C-4. 
Composition B is useful as a cast primer. 

Relievers.— \n a heading round, holes adjacent to the cut 
holes, used to expand the opening made by the cut holes. 

Rib holes.— The holes at the sides of a tunnel or drift round, 
which determine the width of the opening. 

Rip rap.— Coarse rocks used for river bank or dam stabiliza- 
tion to reduce erosion by water flow. 

Rotational firing.— A delay blasting system in which each 
charge successively displaces its burden into a void created 
by an explosive detonated on an earlier delay period. 



Round.— A group or set of blastholes required to produce a 
unit of advance in underground headings or tunnels. 



Safety fuse.— A core of potassium nitrate black powder, 
enclosed in a covering of textile and waterproofing, which is 
used to initiate a blasting cap or a black powder charge. Safety 
fuse burns at a continuous, uniform rate. 

Scaled distance.— A ratio used to predict ground vibrations. 
As commonly used in blasting, scaled distance equals the 
distance from the blast to the point of concern, in feet, divided 
by the square root of the charge weight of explosive per delay, 
in pounds. Normally, when using the equation, the delay period 
must be at least 9 ms. 

Secondary blasting.— \Js\ng explosives to break boulders 
or high bottom resulting from the primary blast. 

Seismograph.— An instrument that measures and may sup- 
ply a permanent record of earthborne vibrations induced by 
earthquakes or blasting. 

Semiconductive hose.— A hose, used for pneumatic loading 
of AN-FO, which has a minimum electrical resistance of 1 ,000 
ohms/ft and 10,000 ohms total resistance and a maximum 
total resistance of 2,000,000 ohms. 

Sensitiveness.— A measure of an explosive's ability to propa- 
gate a detonation. 

Sensitivity.— A measure of an explosive's susceptibility to 
detonation upon receiving an external impulse such as impact, 
shock, flame, or friction. 

Sensitizer.— An ingredient used in explosive compounds to 
promote greater ease in initiation or propagation of the detona- 
tion reaction. 

Sequential blasting machine.— A series of condenser dis- 
charge blasting machines in a single unit which can be acti- 
vated at various accurately timed intervals following the 
application of electrical current. 

Series circuit— A circuit of electric blasting caps in which 
each leg wire of a cap is connected to a leg wire from the 
adjacent caps so that the electrical current follows a single 
path through the entire circuit. 

Series-in-parallel circuit.—See parallel series circuit. 

Shatter cut—See parallel hole cut. 

Shelf life.— The length of time for which an explosive can be 
stored without losing its efficient performance characteristics. 

Shock energy.— The shattering force of an explosive caused 
by the detonation wave. 

Shock tube system.— A system for initiating caps in which 
the energy is transmitted to the cap by means of a shock wave 
inside a hollow plastic tube. 

Shock wave.— A pressure pulse that propagates at super- 
sonic velocity. 

Shot— See blast. 

S/Joff/rer.— Also referred to as the shooter. The person who 
actually fires a blast. A powderman, on the other hand, may 
charge or load blastholes with explosives but may not fire the 
blast. 

Shunt.— A piece of metal or metal foil which short circuits 
the ends of cap leg wires to prevent stray currents from caus- 
ing accidental detonation of the cap. 

Silver chloride cell.— A low-current cell used in a blasting 
galvanometer and other devices used to measure continuity in 
electric blasting caps and circuits. 

Slurry.— An aqueous solution of ammonium nitrate, sensi- 
tized with a fuel, thickened, and crosslinked to provide a 
gelatinous consistency. Sometimes called a water gel. DOT 
may classify a sluny as a Class A explosive, a Class B explosive, 
or a blasting agent. An explosive or blasting agent containing 



105 



substantial portions of water (MSHA). See emulsion; water 
gel. 

Smooth blasting.— A method of controlled blasting, used 
underground, in which a series of closely spaced holes is 
drilled at the perimeter, loaded with decoupled charges, and 
fired on the highest delay period of the blast round. 

Snake hole.— A borehole drilled slightly downward from 
horizontal into the floor of a quarry face. Also, a hole drilled 
under a boulder. 

Sodium nitrate.— An oxidizer used in dynamites and some- 
times in blasting agents. 

Spacing.— The distance between boreholes or charges in a 
row, measured perpendicular to the burden and parallel to the 
free face of expected rock movement. 

Specific gravity.— The ratio of the weight of a given volume 
of any substance to the weight of an equal volume of water. 

Spitter cord.— See Ignitacord. 

Springing.— See chambering. 

Square pattern.— A pattern of blastholes in which the holes 
in succeeding rows are drilled directly behind the holes in the 
front row. In a truly square pattern the burden and spacing are 
equal. 

Squib.— A firing device that burns with a flash. Used to 
ignite black powder or pellet powder. 

Stability.— The ability of an explosive material to maintain 
its physical and chemical properties over a period of time in 



Staggered pattern.— A pattern of blastholes in which holes 
in each row are drilled between the holes in the preceding row. 

Static electricity.— E\ec\nca\ energy stored on a person or 
object in a manner similar to that of a capacitor. Static electric- 
ity may be discharged into electrical initiators, thereby detonat- 
ing them. 

Steady state velocity.— The characteristic velocity at which 
a specific explosive, under specific conditions, in a given 
charge diameter, will detonate. 

Stemming.— The inert material, such as drill cuttings, used 
in the collar portion (or elsewhere) of a blasthole to confine the 
gaseous products of detonation. Also, the length of blasthole 
left uncharged. 

Stick count.— See cartridge count. 

Stray currenf.— Current flowing outside its normal conductor. 
A result of defective insulation, it may come from electrical 
equipment, electrified fences, electric railways, or similar items. 
Flow is facilitated by conductive paths such as pipelines and 
wet ground or other wet materials. Galvanic action of two 
dissimilar metals, in contact or connected by a conductor, may 
cause stray current. 

Strength.— A property of an explosive described in various 
terms such as cartridge or weight strength, seismic strength, 
shock or bubble energy, crater strength, ballistic mortar strength, 
etc. Not a well-defined property. Used to express an explosive's 
capacity to do work. 

String loading.— The procedure of loading cartridges end to 
end in a borehole without deforming them. Used mainly in 
controlled blasting and permissible blasting. 

Subdrill.— To drill blastholes beyond the planned grade lines 
or below floor level to insure breakage to the planned grade or 
floor level. 

Subson/c. —Slower than the speed of sound. 

St/person/c— Faster than the speed of sound. 

Swell factor.— The ratio of the volume of a material in its 
solid state to that when broken. May also be expressed as the 
reciprocal of this number. 



Sympathetic propagation (sympathetic detonation).— 
Detonation of an explosive material by means of an impulse 
from another detonation through air, earth, or water. 



Tamping.— The process of compressing the stemming or explo- 
sive in a blasthole. Sometimes used synonymously with 
stemming. 

Tamping bag.— A cylindrical bag containing stemming 
material, used to confine explosive charges in boreholes. 

Tamping pole.— See loading pole. 

Tesf blasting cap No. 8.— A detonator containing 0.40 to 
0.45 g of PETN base charge at a specific gravity of 1 .4 g/cu 
cm , and primed with standard weights of primer, depending on 
the manufacturer. 

7be.— The burden or distance between the bottom of a 
borehole and the vertical free face of a bench in an excavation. 
Also the rock left unbroken at the foot of a quarry blast. 

Transient velocity.— A velocity, different from the steady 
state velocity, which a primer imparts to a column of powder. 
The powder column quickly attains steady state velocity. 

Trinitrotoluene (TNT).— A military explosive compound used 
industrially as a sensitizer for slurries and as an ingredient in 
pentolite and composition B. Once used as a free-running 
pelletized powder. 

Trunkline.—A detonating cord line used to connect the 
downlines or other detonating cord lines in a blast pattern. 
Usually runs along each row of blastholes. 

Tunnel.— A horizontal underground passage. 

Two-component explosive.— See binary explosive. 



Unconfined detonation velocity.— The detonation velocity of 
an explosive material not confined by a borehole or other 
confining medium. 



V-cut.—A cut employing several pairs of angled holes, meet- 
ing at the bottoms, used to create free faces for the rest of the 
blast round. 

Velocity.— The rate at which the detonation wave travels 
through an explosive. May be measured confined or unconfined. 
Manufacturer's data are sometimes measured with explo- 
sives confined in a steel pipe. 

Venturi loader.— See jet loader. 

Volume strength.— See cartridge strength or bulk strength. 



Waterge/.— An aqueoussolution of ammonium nitrate, sensi- 
tized with a fuel, thickened, and crosslinked to provide a 
gelatinous consistency. Also called a slurry. May be an explo- 
sive or a blasting agent. 

IVaterres/sfance.— A qualitative measure of the ability of an 
explosive or blasting agent to withstand exposure to water 
without becoming deteriorated or desensitized. 

V\/ater stemming bags.— Plastic bags containing a self-sealing 
device, which are filled with water. Classified as a permissible 
stemming device by MSHA. 

Weight strength.— A rating that compares the strength of a 
given weight of explosive with an equivalent weight of straight 
nitroglycerin dynamite, or other explosive standard, expressed 
as a percentage. 



»U.S. GOVERNMENT PRINTING OFPICE : 1985 O-401-4S6/876 



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